Sulfide solid electrolyte and treatment method therefor

ABSTRACT

A sulfide solid electrolyte, which is able to adjust the morphology unavailable traditionally, or is readily adjusted so as to have a desired morphology, the sulfide solid electrolyte having a volume-based average particle diameter measured by laser diffraction particle size distribution measurement of 3 μm or more and a specific surface area measured by the BET method of 20 m2/g or more; and a method of treating a sulfide solid electrolyte including the sulfide solid electrolyte being subjected to at least one mechanical treatment selected from disintegration and granulation.

TECHNICAL FIELD

The present invention relates to a sulfide solid electrolyte and atreatment method therefor.

BACKGROUND ART

With rapid spread of information-related instruments, communicationinstruments, and so on, such as personal computers, video cameras, andmobile phones, in recent years, development of batteries that areutilized as a power source therefor is considered to be important.Heretofore, in batteries to be used for such an application, anelectrolytic solution containing a flammable organic solvent has beenused. However, development of batteries having a solid electrolyte layerin place of an electrolytic solution is being made in view of the factthat by making the battery fully solid, simplification of a safety unitmay be realized without using a flammable organic solvent within thebattery, and the battery is excellent in manufacturing costs andproductivity.

From the viewpoint of performance and production of all-solid-statelithium batteries, a solid electrolyte having a small particle diameteris demanded. In all-solid-state lithium batteries, all of a positiveelectrode material, a negative electrode material, and an electrolyteare solid, and therefore, when the particle diameter of the solidelectrolyte is small, there is an advantage such that it becomes easy toform a contact interface between the active material and the solidelectrolyte, and a pass between ionic conduction and electronicconduction becomes favorable. As a method for making the particlediameter small (also referred to as “atomization”), for example, aproduction method including steps of adding an ether compound to acoarse particle material of a sulfide solid electrolyte material andatomizing the coarse particle material through pulverization treatment(see, for example, PTL 1) is disclosed; and it is disclosed that aparticle of a solid electrolyte having a BET specific surface area of1.8 to 19.7 m²/g, which is used in an all-solid-state lithium ionsecondary battery, is obtained through atomization and heating steps(see, for example, PTL 2).

CITATION LIST Patent Literature

PTL 1: JP 2013-020894 A

PTL 2: WO 2018/193992 A

SUMMARY OF INVENTION Technical Problem

However, in the method of atomization according to, for example, PTLs 1and 2, in order to suppress such properties that on pulverizing a coarseparticle, though granulation (particle growth) is liable to begenerated, a dispersant is added, there is a case where a lowering of anionic conductivity of the solid electrolyte is caused due to the factthat the dispersant remains. In addition, in order to atomize the coarseparticle, a large pulverization energy is required, whereby thecrystallinity is reduced. For that reason, the crystallinity is enhancedupon heating; however, there is involved such a problem that in order tocontemplate to enhance the crystallinity, granulation (particle growth)is generated, and in order to contemplate to suppress the granulation(particle growth), sufficient granulation is not obtained.

A desirable optimum morphology of the solid electrolyte, such asparticle diameter, varies with a positive electrode material, a negativeelectrode material, and an electrolyte of the all-solid-state lithiumbattery. However, according to the conventional method for atomizing thecoarse particle, as mentioned previously, the reduction of crystallinityowing to a large pulverization energy and the granulation duringre-heating treatment must be adjusted by setting the respectiveconditions. This adjustment is extremely difficult, and furthermore, theproduction costs further increase, and therefore, it may not be saidthat the foregoing method is a realistic method on an industrial scale.

In view of the aforementioned circumstances, the present invention hasbeen made, and an object thereof is to provide a sulfide solidelectrolyte that is a precursor for mechanical treatment which is ableto adjust the morphology unavailable traditionally, or is readilyadjusted so as to have a desired morphology and further a treatmentmethod of a solid electrolyte, in which this is subjected to mechanicaltreatment, thereby enabling one to adjust the morphology.

Solution to Problem

In order to solve the aforementioned problem, the present inventor madeextensive and intensive investigations. As a result, it has been foundthat the foregoing problem can be solved by the following inventions.

1. A sulfide solid electrolyte having a volume-based average particlediameter measured by laser diffraction particle size distributionmeasurement of 3 μm or more and a specific surface area measured by theBET method of 20 m²/g or more.

2. A treatment method of a sulfide solid electrolyte, includingsubjecting a sulfide solid electrolyte having a volume-based averageparticle diameter measured by laser diffraction particle sizedistribution measurement of 3 μm or more and a specific surface areameasured by the BET method of 20 m²/g or more to at least one mechanicaltreatment selected from disintegration and granulation.

Advantageous Effects of Invention

In accordance with the present invention, a sulfide solid electrolytewhich is able to adjust the morphology unavailable traditionally, or isreadily adjusted so as to have a desired morphology and further atreatment method of a sulfide solid electrolyte, in which this issubjected to mechanical treatment, thereby enabling one to adjust themorphology, can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flow chart of explaining one example of preferredembodiments of a production method of a precursor for mechanicaltreatment.

FIG. 2 is a flow chart of explaining one example of preferredembodiments of a production method of a precursor for mechanicaltreatment.

FIG. 3 is an X-ray diffraction spectrum of each of an electrolyteprecursor, an amorphous solid electrolyte, and a crystalline solidelectrolyte obtained in Example 1.

FIG. 4 is an X-ray diffraction spectrum of each of raw materials used inExamples.

FIG. 5 is an X-ray diffraction spectrum of each of an amorphous sulfidesolid electrolyte and a crystalline sulfide solid electrolyte obtainedin Example 1.

FIG. 6 is a graph showing a relation between a particle diameter and aspecific surface area of each of sulfide solid electrolytes obtained inExamples.

FIG. 7 is a photographed image by a scanning electron microscope (SEM)of a sulfide solid electrolyte obtained in Example 5.

FIG. 8 is a photographed image by a scanning electron microscope (SEM)of a sulfide solid electrolyte obtained in Example 6.

FIG. 9 is a photographed image by a scanning electron microscope (SEM)of a sulfide solid electrolyte obtained in Example 7.

DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention (in this specification, theembodiment will be sometimes referred to as “present embodiment”) arehereunder described. In this specification, numerical values of an upperlimit and a lower limit according to numerical value ranges of “ormore”, “or less”, and “XX to YY” are each a numerical value which can bearbitrarily combined, and numerical values of the section of Examplescan also be used as numerical values of an upper limit and a lowerlimit, respectively.

[Sulfide Solid Electrolyte]

The sulfide solid electrolyte of the present embodiment is one having avolume-based average particle diameter measured by laser diffractionparticle size distribution measurement of 3 μm or more (in thisspecification, the foregoing average particle diameter will be sometimesreferred to simply as “average particle diameter”) and a specificsurface area measured by the BET method of 20 m²/g or more (in thisspecification, the foregoing specific surface area will be sometimesreferred to simply as “specific surface area”).

Although the sulfide solid electrolyte of the present embodiment is ableto be used for a sulfide solid electrolyte as it stands, when allowingit to have the predetermined volume-based average particle diameter andspecific surface area, the sulfide solid electrolyte of the presentembodiment becomes extremely suitable as a precursor for mechanicaltreatment for adjusting the morphology through at least one mechanicaltreatment selected from disintegration and granulation (in thisspecification, the foregoing mechanical treatment will be sometimesreferred to simply as “mechanical treatment”) (in this specification,the foregoing precursor for mechanical treatment will be sometimesreferred to simply as “precursor for mechanical treatment”).Accordingly, it is preferred that the sulfide solid electrolyte of thepresent embodiment is used as the precursor for mechanical treatment.Here, in this specification, the term “morphology” means variousproperties which the solid electrolyte particle has, and in particular,it is an average particle diameter and a specific surface that areproperties required regarding the production of a solid electrolyte.

When the volume-based average particle diameter falls within theaforementioned relatively large range, in general, an interface betweenthe solid electrolytes is hardly taken, so that a favorable batteryperformance is hardly obtained; and when the specific surface area fallswithin the aforementioned relatively large range, on the occasion offorming a slurry, the viscosity is liable to become high, and the slurrycoating properties become worse, so that a lowering of the productionefficiency of an all-solid-state lithium battery is liable to begenerated. However, in view of the fact that the aforementioned averageparticle diameter and specific surface area are provided, andespecially, the specific surface area is relatively large, the precursorfor mechanical treatment has a porous structure, and therefore, it hasproperties such that in order to provide a solid electrolyte in whicheven when applying a smaller energy, it is readily collapsed and has thedesired morphology, disintegration (atomization) and granulation(particle growth) through mechanical treatment are readily achieved. Inaddition, in view of the fact that a small energy is sufficient, itbecomes possible to widely select an instrument to be used for themechanical treatment.

FIG. 6 shows a relation between an average particle diameter and aspecific surface area in the case of subjecting each of precursors formechanical treatment of the present embodiment (Examples 1 to 20) tomechanical treatment. The numerical values in the figure expressExamples 5 to 7, 10, and 11, respectively as described below. Inaddition, FIGS. 7 to 9 are each of photographed images by a scanningelectron microscope (SEM) of sulfide solid electrolytes after mechanicaltreatment of precursors for mechanical treatment of Examples 5, 6, and7, respectively.

According to conventional sulfide solid electrolytes, since the particleshape is not a true sphere, the relation between the particle diameterand the specific surface area is established within a range where thoughit does not coincide with a theoretical line, in general, it does notlargely deviate from the theoretical line.

On the other hand, the precursor for mechanical treatment of the presentembodiment has a morphology largely deviating from the theoretical line.This is because as shown in FIG. 7 (Example 5), the precursor formechanical treatment has a structure composed of secondary particlesresulting from aggregation of fine primary particles. According to thisstructure, when the mechanical treatment is performed with a relativelysmall energy, the average particle diameter becomes close to that ofprimary particles owing to disintegration of secondary particles as seenin from Example 5 to Example 6, and the specific surface area does notsubstantially change (see FIG. 8). Conversely, when the mechanicaltreatment is performed with a relatively large energy, the primaryparticles are gathered each other and granulated at the same time ofdisintegration of the secondary particles as shown in FIG. 9 (Example7), whereby both the particle diameter and the specific surface areabecome small.

In addition, by adjusting the energy of the mechanical treatment, forexample, it becomes possible to control the morphology such that afterundergoing the disintegration of secondary particles, the granulationtakes place as seen in from Example 10 to Example 11 (fromdisintegration with a low energy to granulation with a high energy).

In the light of the above, though as a matter of course, the sulfidesolid electrolyte of the present embodiment can be used for a sulfidesolid electrolyte as it stands, it may be considered that the sulfidesolid electrolyte of the present embodiment becomes a precursor formechanical treatment, which is suitably used for the mechanicaltreatment especially for the purpose of adjusting the morphology throughthe mechanical treatment. Then, by using, as the precursor formechanical treatment, the sulfide solid electrolyte having properties ofreadily adjusting the morphology, it has become possible to easilyseparately make a positive electrode material, a negative electrodematerial, and a solid electrolyte to be used for the electrolyte of anall-solid-state lithium battery in which the morphology of the solidelectrolyte, for example, a desirable optimum particle diameter, isdifferent.

(Properties of Sulfide Solid Electrolyte)

The sulfide solid electrolyte of the present embodiment is one having avolume-based average particle diameter measured by laser diffractionparticle size distribution measurement of 3 μm or more. From theviewpoint of easy adjustment of morphology, the average particlediameter is preferably 4 μm or more, more preferably 5 μm or more, andstill more preferably 7 μm or more, and an upper limit thereof ispreferably 150 μm or less, more preferably 125 μm or less, still morepreferably 100 μm or less, and yet still more preferably 50 μm or less.

In this specification, the average particle diameter by laserdiffraction particle size distribution measurement is a particlediameter to reach 50% of all the particles in sequential cumulation fromthe smallest particles in drawing the particle diameter distributioncumulative curve, and the volume distribution is concerned with anaverage particle diameter which can be, for example, measured with alaser diffraction/scattering particle diameter distribution measuringdevice. In this specification, the average particle diameter is alsoreferred to as “average particle diameter (D₅₀)”.

More specifically, the average particle diameter is, for example,measured in the following manner.

First of all, 110 mL of dehydrated toluene (manufactured by Wako PureChemical Industries, Ltd., a product name: Special Grade) is charged ina dispersing tank of a laser diffraction particle size distributionmeasuring device, and 6% of dehydrated tertiary butyl alcohol(manufactured by Wako Pure Chemical Industries, Ltd., Special Grade) asa dispersant is further added.

The aforementioned mixture is thoroughly mixed, to which is then added adried sulfide solid electrolyte, and the particle diameter is measured.The addition amount of the dried sulfide solid electrolyte is adjustedand added such that the laser scattering intensity corresponding to theparticle concentration in an operation screen in the measuring devicefalls within a prescribed range (10 to 20%). When the addition amount ismore than this range, there is a concern that multiple scattering isgenerated, whereby the precise particle diameter distribution cannot bedetermined. In addition, when the addition amount is lower than thisrange, there is a concern that the SN ratio becomes worse, whereby theprecise measurement cannot be achieved. The scattering intensity isindicated on a basis of the addition amount of the “dried sulfide solidelectrolyte” according to a measuring device, and therefore, theaddition amount at which the aforementioned laser scattering intensityfalls within the aforementioned range may be found.

Although an optimum amount of the addition amount of the “dried sulfidesolid electrolyte” varies with the kind and particle diameter, etc. of ametal salt, it is generally about 0.005 g to 0.05 g.

In addition, the sulfide solid electrolyte of the present embodiment isone having a specific surface area measured by the BET method of 20 m²/gor more. From the viewpoint of easy adjustment of morphology, thespecific surface area is preferably 21 m²/g or more, more preferably 23m²/g or more, still more preferably 25 m²/g or more, and yet still morepreferably 27 m²/g or more, and an upper limit thereof is preferably 70m²/g or less, more preferably 60 m²/g or less, still more preferably 50m²/g or less, and yet still more preferably 35 m²/g or less.

In this specification, the specific surface area is a value measured bythe BET method (gas adsorption method), and as the gas, nitrogen may beused (nitrogen method), or krypton may be used (krypton method). The gasis appropriately selected according to the size of the specific surfacearea and provided for the measurement. The specific surface area can be,for example, measured using a commercially available device, such as agas adsorption measuring device (for example, AUTOSORB 6 (manufacturedby Sysmex Corporation)).

The sulfide solid electrolyte of the present embodiment contains atleast a sulfur element and preferably contains a lithium element as anelement for revealing the ionic conductivity, and from the viewpoint ofenhancing the ionic conductivity, it preferably contains a phosphoruselement and a halogen element.

The sulfide solid electrolyte of the present embodiment is preferablyone containing a thio-LISICON Region II-type crystal structure. The“solid electrolyte” and “crystalline solid electrolyte” in thisspecification are mentioned later. When the present crystal structure iscontained, the sulfide solid electrolyte of the present embodiment maybecome a solid electrolyte having a high ionic conductivity.

While a blending ratio of these various elements will be described indetail in the production method of a sulfide solid electrolyte(production method of a precursor for mechanical treatment) as mentionedlater, a blending ratio (molar ratio) of lithium element to sulfurelement to phosphorous element to halogen atom is preferably (1.0 to1.8)/(1.0 to 2.0)/(0.1 to 0.8)/(0.01 to 0.6), more preferably (1.1 to1.7)/(1.2 to 1.8)/(0.2 to 0.6)/(0.05 to 0.5), and still more preferably(1.2 to 1.6)/(1.3 to 1.7)/(0.25 to 0.5)/(0.08 to 0.4).

In addition, in the case of using a combination of bromine and iodine asthe halogen element, a blending ratio (molar ratio) of lithium elementto sulfur element to phosphorus element to bromine to iodine ispreferably (1.0 to 1.8)/(1.0 to 2.0)/(0.1 to 0.8)/(0.01 to 3.0)/(0.01 to0.3), more preferably (1.1 to 1.7)/(1.2 to 1.8)/(0.2 to 0.6)/(0.02 to0.25)/(0.02 to 0.25), still more preferably (1.2 to 1.6)/(1.3 to1.7)/(0.25 to 0.5)/(0.03 to 0.2)/(0.03 to 0.2), and yet still morepreferably (1.35 to 1.45)/(1.4 to 1.7)/(0.3 to 0.45)/(0.04 to0.18)/(0.04 to 0.18). By allowing the blending ratio (molar ratio) oflithium element to sulfur element to phosphorus element to halogenelement to fall within the aforementioned range, it becomes easy toprovide a solid electrolyte having a thio-LISICON Region II-type crystalstructure and having a higher ionic conductivity.

[Production Method of Sulfide Solid Electrolyte]

Although a production method of the aforementioned sulfide solidelectrolyte to be used as the precursor for mechanical treatment is notparticularly restricted, from the viewpoint of obtaining not only thepredetermined average particle diameter and specific surface area whichthe sulfide solid electrolyte of the present embodiment has but also ahigher ionic conductivity, it is preferred to include mixing the rawmaterial inclusion containing a lithium element, a sulfur element, aphosphorus element, and a halogen element with a complexing agent. Inthis specification, in order to distinguish the “production method ofthe aforementioned sulfide solid electrolyte to be used as the precursorfor mechanical treatment” from a treatment method of the solidelectrolyte of the present embodiment as mentioned later, it issometimes referred to simply as “production method of a precursor formechanical treatment”, “present production method”, or the like.

The “solid electrolyte” as referred to in this specification means anelectrolyte of keeping the solid state at 25° C. in a nitrogenatmosphere. The solid electrolyte in the present embodiment is a solidelectrolyte containing a lithium element, a sulfur element, a phosphoruselement, and a halogen element and having an ionic conductivity to becaused owing to the lithium element. In view of the fact that the solidelectrolyte in the present embodiment contains the sulfur element, it isalso referred to as “sulfide solid electrolyte”.

In the “solid electrolyte”, both of a crystalline solid electrolytehaving a crystal structure and an amorphous solid electrolyte areincluded. The crystalline solid electrolyte as referred to in thisspecification is a material that is a solid electrolyte in which peaksderived from the solid electrolyte are observed in an X-ray diffractionpattern in the X-ray diffractometry, and the presence or absence ofpeaks derived from the raw materials of the solid electrolyte does notmatter. That is, the crystalline solid electrolyte contains a crystalstructure derived from the solid electrolyte, in which a part thereofmay be a crystal structure derived from the solid electrolyte, or all ofthem may be a crystal structure derived from the solid electrolyte. Thecrystalline solid electrolyte may be one in which an amorphous solidelectrolyte is contained in a part thereof so long as it has the X-raydiffraction pattern as mentioned above. In consequence, in thecrystalline solid electrolyte, a so-called glass ceramics which isobtained by heating the amorphous solid electrolyte to a crystallizationtemperature or higher is contained.

The amorphous solid electrolyte as referred to in this specification isa halo pattern in which other peak than the peaks derived from thematerials is not substantially observed in an X-ray diffraction patternin the X-ray diffractometry, and it is meant that the presence orabsence of peaks derived from the raw materials of the solid electrolytedoes not matter.

In the production method of a precursor for mechanical treatment, thereare included the following four embodiments depending upon whether ornot a solid electrolyte, such as Li₃PS₄, is used as the raw material,and whether or not a solvent is used. Examples of preferred modes ofthese four embodiments are shown in FIG. 1 (Embodiments A and B) andFIG. 2 (Embodiments C and D). That is, in the present production method,there are preferably included a production method of using rawmaterials, such as lithium sulfide and diphosphorus pentasulfide, and acomplexing agent (Embodiment A); a production method of containing, asraw materials, Li₃PS₄ that is an electrolyte main structure, and thelike and using a complexing agent (Embodiment B); a production method ofadding a solvent to the raw materials, such as lithium sulfide, and thecomplexing agent in the aforementioned Embodiment A (Embodiment C); anda production method of adding a solvent to the raw materials, such asLi₃PS₄, and the complexing agent in the aforementioned Embodiment B(Embodiment D).

The Embodiments A to D are hereunder described in order.

Embodiment A

As shown in FIG. 1, the Embodiment A is concerned with a mode in whichin a production method including mixing a raw material inclusioncontaining a lithium element, a sulfur element, a phosphorus element,and a halogen element with a complexing agent, lithium sulfide anddiphosphorus pentasulfide, and the like are used as the raw materialinclusion. By mixing the raw material inclusion with the complexingagent, in general, an electrolyte precursor inclusion that is asuspension is obtained, and by drying it, the electrolyte precursor isobtained. Furthermore, by heating the electrolyte precursor, thecrystalline solid electrolyte is obtained. In addition, while notillustrated, it is preferred that the before heating, the electrolyteprecursor is pulverized, and an electrolyte precursor pulverized productobtained through pulverization is heated. That is, the presentproduction method preferably includes mixing; pulverization of theelectrolyte precursor obtained through mixing; and heating of theelectrolyte precursor pulverized product obtained through pulverization.While the description is hereunder made beginning from Embodiment A, onedescribed with the wordings “of the present embodiment” is a matterapplicable even in other embodiments.

(Raw Material Inclusion)

The raw material inclusion which is used in the present embodiment isone containing a lithium element, a sulfur element, a phosphoruselement, and a halogen element.

As the raw materials to be contained in the raw material inclusion, forexample, a compound containing at least one of a lithium element, asulfur element, a phosphorus element, and a halogen element can be used.More specifically, representative examples of the foregoing compoundinclude raw materials composed of at least two elements selected fromthe aforementioned four elements, such as lithium sulfide; lithiumhalides, e.g., lithium fluoride, lithium chloride, lithium bromide, andlithium iodide; phosphorus sulfides, e.g., diphosphorus trisulfide(P₂S₃) and diphosphorus pentasulfide (P₂S₅); phosphorus halides, e.g.,various phosphorus fluorides (e.g., PF₃ and PF₅), various phosphoruschlorides (e.g., PCl₃, PCl₅, and P₂Cl₄), various phosphorus bromides(e.g., PBr₃ and PBr₅), and various phosphorus iodides (e.g., PI₃ andP₂I₄); and thiophosphoryl halides, e.g., thiophosphoryl fluoride (PSF₃),thiophosphoryl chloride (PSCl₃), thiophosphoryl bromide (PSBr₃),thiophosphoryl iodide (PSI₃), thiophosphoryl dichlorofluoride (PSCl₂F),and thiophosphoryl dibromofluoride (PSBr₂F), as well as halogen simplesubstances, such as fluorine (F₂), chlorine (C₂), bromine (Br₂), andiodine (I₂), with bromine (Br₂) and iodine (I₂) being preferred.

As materials which may be used as the raw material other than thosementioned above, a compound containing not only at least one elementselected from the aforementioned four elements but also other elementthan the foregoing four elements can be used. More specifically,examples thereof include lithium compounds, such as lithium oxide,lithium hydroxide, and lithium carbonate; alkali metal sulfides, such assodium sulfide, potassium sulfide, rubidium sulfide, and cesium sulfide;metal sulfides, such as silicon sulfide, germanium sulfide, boronsulfide, gallium sulfide, tin sulfide (e.g., SnS and SnS₂), aluminumsulfide, and zinc sulfide: phosphoric acid compounds, such as sodiumphosphate and lithium phosphate; halide compounds of an alkali metalother than lithium, such as sodium halides, e.g., sodium iodide, sodiumfluoride, sodium chloride, and sodium bromide; metal halides, such as analuminum halide, a silicon halide, a germanium halide, an arsenichalide, a selenium halide, a tin halogen, an antimony halide, atellurium halide, and a bismuth halide; and phosphorus oxyhalides, suchas phosphorus oxychloride (POCl₃) and phosphorus oxybromide (POBr₃).

In the Embodiment A, among them, phosphorus sulfides, such as lithiumsulfide, diphosphorus trifluoride (P₂S₃), and diphosphorus pentasulfide(P₂S₅); halogen simple substances, such as fluorine (F₂), chlorine(Cl₂), bromine (Br₂), and iodine (I₂); and lithium halides, such aslithium fluoride, lithium chloride, lithium bromide, and lithium iodideare preferred as the raw material from the viewpoint of more easilyobtaining a solid electrolyte having not only predetermined averageparticle diameter and specific surface area but also a high ionicconductivity. Preferred examples of a combination of raw materialsinclude a combination of lithium sulfide, diphosphorus pentasulfide, anda lithium halide; and a combination of lithium sulfide, phosphoruspentasulfide, and a halogen simple substance, in which the lithiumhalide is preferably lithium bromide or lithium iodide, and the halogensimple substance is preferably bromine or iodine.

The lithium sulfide which is used in the Embodiment A is preferably aparticle.

An average particle diameter (D₅₀) of the lithium sulfide particle ispreferably 10 μm or more and 2,000 μm or less, more preferably 30 μm ormore and 1,500 μm or less, and still more preferably 50 μm or more and1,000 μm or less. Among the above-exemplified raw materials, the solidraw material is preferably one having an average particle diameter ofthe same degree as in the aforementioned lithium sulfide particle,namely one having an average particle diameter falling within the samerange as in the aforementioned lithium sulfide particle is preferred.

In the case of using lithium sulfide, diphosphorus pentasulfide, and thelithium halide as the raw materials, from the viewpoint of obtaininghigher chemical stability and a higher ionic conductivity, a proportionof lithium sulfide relative to the total of lithium sulfide anddiphosphorus pentasulfide is preferably 70 to 80 mol %, more preferably72 to 78 mol %, and still more preferably 74 to 76 mol %.

In the case of using lithium sulfide, diphosphorus pentasulfide, alithium halide, and other raw material to be optionally used, thecontent of lithium sulfide and diphosphorus pentasulfide relative to thetotal of the aforementioned raw materials is preferably 60 to 100 mol %,more preferably 65 to 90 mol %, and still more preferably 70 to 80 mol%.

In the case of using a combination of lithium bromide and lithium iodideas the lithium halide, from the viewpoint of enhancing the ionicconductivity, a proportion of lithium bromide relative to the total oflithium bromide and lithium iodide is preferably 1 to 99 mol %, morepreferably 20 to 90 mol %, still more preferably 40 to 80 mol %, andespecially preferably 50 to 70 mol %.

In the case of using not only a halogen simple substance but alsolithium sulfide and diphosphorus pentasulfide as the raw materials, aproportion of the molar number of lithium sulfide excluding lithiumsulfide having the same molar number as the molar number of the halogensimple substance relative to the total molar number of lithium sulfideand diphosphorus pentasulfide excluding lithium sulfide having the samemolar number as the molar number of the halogen simple substance fallspreferably within a range of 60 to 90%, more preferably within a rangeof 65 to 85%, still more preferably within a range of 68 to 82%, yetstill more preferably within a range of 72 to 78%, and even yet stillmore preferably within a range of 73 to 77%. This is because when theforegoing proportion falls within the aforementioned ranges, a higherionic conductivity is obtained. In addition, in the case of usinglithium sulfide, diphosphorus pentasulfide, and a halogen simplesubstance, from the same viewpoint, the content of the halogen simplesubstance relative to the total amount of lithium sulfide, diphosphoruspentasulfide, and the halogen simple substance is preferably 1 to 50 mol%, more preferably 2 to 40 mol %, still more preferably 3 to 25 mol %,and yet still more preferably 3 to 15 mol %.

In the case of using lithium sulfide, diphosphorus pentasulfide, ahalogen simple substance, and a lithium halide, the content (a mol %) ofthe halogen simple substance and the content (B mol %) of the lithiumhalide relative to the total of the aforementioned raw materialspreferably satisfy the following expression (2), more preferably satisfythe following expression (3), still more preferably satisfy thefollowing expression (4), and yet still more preferably satisfy thefollowing expression (5).

2≤(2α+β)≤100  (2)

4≤(2α+β)≤80  (3)

6≤(2α+β)≤50  (4)

6≤(2α+β)≤30  (5)

In the case of using two halogen simple substances, when the molarnumber in the substance of the halogen element of one side is designatedas A1, and the molar number in the substance of the halogen element ofthe other side is designated as A2, an A1/A2 ratio is preferably (1 to99)/(99 to 1), more preferably 10/90 to 90/10, still more preferably20/80 to 80/20, and yet still more preferably 30/70 to 70/30.

In the case where the two halogen simple substances are bromine andiodine, when the molar number of bromine is designated as B1, and themolar number of iodine is designated as B2, a B1/B2 ratio is preferably(1 to 99)/(99 to 1), more preferably 15/85 to 90/10, still morepreferably 20/80 to 80/20, yet still more preferably 30/70 to 75/25, andespecially preferably 35/65 to 75/25.

(Complexing Agent)

In the present embodiment, a complexing agent is used. The complexingagent as referred to in this specification is a substance capable offorming a complex together with the lithium element and means one havingsuch properties of acting with the lithium element-containing sulfideand the halide, and the like contained in the aforementioned rawmaterials, thereby promoting formation of the electrolyte precursor.

As the complexing agent, any material can be used without beingparticularly restricted so long as it has the aforementioned properties.In particular, elements having a high affinity with the lithium element,for example, compounds containing a hetero element, such as a nitrogenelement, an oxygen element, and a chlorine element, are preferablyexemplified, and compounds having a group containing such a heteroelement are more preferably exemplified. This is because such a heteroelement and the group containing the foregoing hetero element may becoordinated (bound) with lithium.

It may be considered that with respect to the complexing agent, thehetero element in the molecule thereof has a high affinity with thelithium element, and the complexing agent has such properties of bindingwith the lithium-containing structure which is existent as a mainstructure in the solid electrolyte obtained by the present productionmethod, such as Li₃PS₄ containing representatively a PS₄ structure, andthe lithium-containing raw materials, such as a lithium halide, therebyeasily forming an aggregate. For that reason, since by mixing theaforementioned raw material inclusion and the complexing agent, anaggregate via the lithium-containing structure, such as a PS₄ structure,or the complexing agent, and an aggregate via the lithium-containing rawmaterial, such as a lithium halide, or the complexing agent are evenlyexistent, whereby an electrolyte precursor in which the halogen elementis more likely dispersed and fixed is obtained, as a result, it may beconsidered that a solid electrolyte having a high ionic conductivity, inwhich the generation of hydrogen sulfide is suppressed, is obtained. Inaddition, it may be considered that the predetermined average particlediameter and specific surface area are readily obtained.

In consequence, the complexing agent preferably has at least two heteroelements capable of being coordinated (bound) therewith in the molecule,and more preferably has at least two hetero element-containing groups inthe molecule. In view of the fact that the complexing agent has at leasttwo hetero element-containing groups in the molecule, thelithium-containing structure, such as Li₃PS₄ containing a PS₄ structure,and the lithium-containing raw material, such as a lithium halide, canbe bound with each other via the at least two hetero elements in themolecule, the halogen element is more likely dispersed and fixed in theelectrolyte precursor. As a result, a solid electrolyte having not onlypredetermined average particle diameter and specific surface area butalso a high ionic conductivity, in which the generation of hydrogensulfide is suppressed, is obtained. In addition, among the heteroelements, a nitrogen element is preferred, and an amino group ispreferred as the group containing a nitrogen element, namely thecomplexing agent is preferably an amine compound.

The amine compound is not particularly restricted so long as it has anamino group in the molecule because it may promote formation of theelectrolyte precursor. However, a compound having at least two aminogroups in the molecule is preferred. In view of the fact that thecomplexing agent has such a structure, the lithium-containing structure,such as Li₃PS₄ containing a PS₄ structure and the lithium-containing rawmaterial, such as a lithium halide, can be bound with each other via atleast two nitrogen elements in the molecule, the halogen element is morelikely dispersed and fixed in the electrolyte precursor. As a result, asolid electrolyte having not only predetermined average particlediameter and specific surface area but also a high ionic conductivity isobtained.

Examples of such an amine compound include amine compounds, such asaliphatic amines, alicyclic amines, heterocyclic amines, and aromaticamines, and these amine compounds can be used alone or in combination ofplural kinds thereof.

More specifically, as the aliphatic amine, aliphatic primary diamines,such as ethylenediamine, diaminopropane, and diaminobutane; aliphaticsecondary diamines, such as N,N′-dimethylethylenediamine,N,N′-diethylethylenediamine, N,N′-dimethyldiaminopropane, andN,N′-diethyldiaminopropane; and aliphatic tertiary diamines, such asN,N,N′,N′-tetramethyldiaminomethane,N,N,N′,N′-tetramethylethylenediamine,N,N,N′,N′-tetraethylethylenediamine,N,N,N′,N′-tetramethyldiaminopropane, N,N,N′,N′-tetraethyldiaminopropane,N,N,N′,N′-tetramethyldiaminobutane, N,N,N′,N′-tetramethyldiaminopentane,and N,N,N′,N′-tetramethyldiaminohexane, are representatively preferablyexemplified. Here, in the exemplification in this specification, forexample, when the diaminobutane is concerned, it should be construedthat all of isomers inclusive of not only isomers regarding the positionof the amino group, such as 1,2-diaminobutane, 1,3-diaminobutane, and1,4-diaminobutane, but also linear or branched isomers and so onregarding the butane are included unless otherwise noted.

The carbon number of the aliphatic amine is preferably 2 or more, morepreferably 4 or more, and still more preferably 6 or more, and an upperlimit thereof is preferably 10 or less, more preferably 8 or less, andstill more preferably 7 or less. In addition, the carbon number of thehydrocarbon group of the aliphatic hydrocarbon group in the aliphaticamine is preferably 2 or more, and an upper limit thereof is preferably6 or less, more preferably 4 or less, and still more preferably 3 orless.

As the alicyclic amine, alicyclic primary diamines, such ascyclopropanediamine and cyclohexanediamine; alicyclic secondarydiamines, such as bisaminomethylcyclohexane; and alicyclic tertiarydiamines, such as N,N,N′,N′-tetramethyl-cyclohexanediamine andbis(ethylmethylamino)cyclohexane, are representatively preferablyexemplified. As the heterocyclic diamine, heterocyclic primary diamines,such as isophoronediamine; heterocyclic secondary diamines, such aspiperazine and dipiperidylpropane; and heterocyclic tertiary diamines,such as N,N-dimethylpiperazine and bismethylpiperidylpropane, arerepresentatively preferably exemplified.

The carbon number of each of the alicyclic amine and the heterocyclicamine is preferably 3 or more, and more preferably 4 or more, and anupper limit thereof is preferably 16 or less, and more preferably 14 orless.

As the aromatic amine, aromatic primary diamines, phenyldiamine,tolylenediamine, and naphthalenediamine; aromatic secondary diamines,such as N-methylphenylenediamine, N,N′-dimethylphenylenediamine,N,N′-bismethylphenylphenylenediamine,N,N′-dimethylnaphthalenediamine,and N-naphthylethylenediamine; and aromatic tertiary diamines, such asN,N-dimethylphenylenediamine, N,N,N′,N′-tetramethylphenylenediamine,N,N,N′,N′-tetramethyldiaminodiphenylmethane, andN,N,N′,N′-tetramethylnaphthalenediamine, are representatively preferablyexemplified.

The carbon number of the aromatic amine is preferably 6 or more, morepreferably 7 or more, and still more preferably 8 or more, and an upperlimit thereof is preferably 16 or less, more preferably 14 or less, andstill more preferably 12 or less.

The amine compound which is used in the present embodiment may also beone substituted with a substituent, such as an alkyl group, an alkenylgroup, an alkoxy group, a hydroxy group, and a cyano group, or a halogenatom.

While the diamines have been exemplified as specific examples, needlessto say, the amine compound which may be used in the present embodimentis not limited to the diamines. Examples thereof include trimethylamine,triethylamine, ethyldimethylamine, aliphatic monoamines corresponding tovarious diamines, such as the aforementioned aliphatic diamines,piperidine compounds, such as piperidine, methylpiperidine, andtetramethylpiperidine, pyridine compounds, such as pyridine andpicoline, morpholine compound, such as morpholine, methylmorpholine, andthiomorpholine, imidazole compounds, such as imidazole andmethylimidazole, alicyclic monoamines, such as monoamines correspondingto the aforementioned alicyclic diamines, and monoamines, such asaromatic monoamines corresponding to the aforementioned aromaticdiamines. Besides, for example, polyamines having three or more aminogroups, such as diethylenetriamine, N,N′,N″-trimethyldiethylenetriamine,N,N,N′,N″,N″-pentamethyldiethylenetriamine, triethylenetetramine,N,N′-bis[(dimethylamino)ethyl]-N,N′-dimethylethylenediamine,hexamethylenetetramine, and tetraethylenepentamine, can also be used.

Among those described above, from the viewpoint of obtaining not onlypredetermined average particle diameter and specific surface area butalso a high ionic conductivity, a tertiary amines having a tertiaryamino group as the amino group are preferred, tertiary diamines havingtwo tertiary amino groups are more preferred, tertiary diamines havingtwo tertiary amino groups on the both ends are still more preferred, andaliphatic tertiary diamines having a tertiary amino group on the bothends are yet still more preferred. In the aforementioned aminecompounds, as the aliphatic tertiary diamine having a tertiary aminogroup on the both ends, tetramethylethylenediamine,tetraethylethylenediamine, tetramethyldiaminopropane, andtetraethyldiaminopropane are preferred, and taking into account easinessof availability and so on, tetramethylethylenediamine andtetramethyldiaminopropane are preferred.

As other complexing agent than the amine compound, for example, acompound having a group containing a hetero element, such as a halogenelement, e.g., an oxygen element and a chlorine element, is high in anaffinity with the lithium element, and such a compound is exemplified asthe other complexing agent than the amine compound. In addition, acompound having a group containing, as the hetero element, a nitrogenelement other than the amino group, for example, a nitro group and anamide group, provides the same effects.

Examples of the other complexing agent include alcohol-based solvents,such as ethanol and butanol; ester-based solvents, such as ethyl acetateand butyl acetate; aldehyde-based solvents, such as formaldehyde,acetaldehyde, and dimethylformamide; ketone-based solvents, such asacetone and methyl ethyl ketone; ether-based solvents, such as diethylether, diisopropyl ether, dibutyl ether, tetrahydrofuran,dimethoxyethane, cyclopentyl methyl ether, tert-butyl methyl ether, andanisole; halogen element-containing aromatic hydrocarbon solvents, suchas trifluoromethylbenzene, nitrobenzene, chlorobenzene, chlorotoluene,and bromobenzene; and solvents containing a carbon atom and a heteroatom, such as acetonitrile, dimethyl sulfoxide, and carbon disulfide. Ofthese, ether-based solvents are preferred; diethyl ether, diisopropylether, dibutyl ether, and tetrahydrofuran are more preferred; anddiethyl ether, diisopropyl ether, and dibutyl ether are still morepreferred.

(Mixing)

As shown in the flow chart of FIG. 1, the raw material inclusion and thecomplexing agent are mixed. In the present embodiment, though a mode ofmixing the raw material inclusion and the complexing agent may be in anyof a solid state and a liquid state, in general, the raw materialinclusion contains a solid, whereas the complexing agent is in a liquidstate, and therefore, in general, mixing is made in a mode in which thesolid raw material inclusion is existent in the liquid complexing agent.

The content of the raw material inclusion is preferably 5 g or more,more preferably 10 g or more, still more preferably 30 g or more, andyet still more preferably 50 g or more relative to the amount of oneliter of the complexing agent, and an upper limit thereof is preferably500 g or less, more preferably 400 g or less, still more preferably 300g or less, and yet still more preferably 250 g of less. When the contentof the raw material inclusion falls within the aforementioned range, theraw material inclusion is readily mixed, the dispersing state of the rawmaterials is enhanced, and the reaction among the raw materials ispromoted, and therefore, the electrolyte precursor and further the solidelectrolyte are readily efficiently obtained.

A method for mixing the raw material inclusion and the complexing agentis not particularly restricted, and the raw materials contained in theraw material inclusion and the complexing agent may be charged in anapparatus capable of mixing the raw material inclusion and thecomplexing agent and mixed. For example, by feeding the complexing agentinto a tank, actuating an impeller, and then gradually adding the rawmaterials, a favorable mixing state of the raw material inclusion isobtained, and dispersibility of the raw materials is enhanced, and thus,such is preferred.

In the case of using a halogen simple substance as the raw material,there is a case where the raw material is not a solid. Specifically,fluorine and chlorine are a gas, and bromine is a liquid under normaltemperature and normal pressure. For example, in the case where the rawmaterial is a liquid, it may be fed into the tank separately from theother raw materials together with the complexing agent, and in the casewhere the raw material is a gas, the raw material may be fed such thatit is blown into the complexing agent having the solid raw materialsadded thereto.

The present embodiment is characterized by including mixing the rawmaterial inclusion and the complexing agent, and the electrolyteprecursor can also be produced by a method not using an instrument to beused for the purpose of pulverization of solid raw materials, which isgenerally called a pulverizer, such as a medium type pulverizer, e.g., aball mill and a bead mill. According to the present production method,by merely mixing the raw material inclusion and the complexing agent,the raw materials and the complexing agent contained in the inclusionare mixed, whereby the electrolyte precursor can be formed. In view ofthe fact that a mixing time for obtaining the electrolyte precursor canbe shortened, or atomization can be performed, the mixture of the rawmaterial inclusion and the complexing agent may be pulverized by apulverizer.

Examples of an apparatus for mixing the raw material inclusion and thecomplexing agent include a mechanical agitation type mixer having animpeller provided in a tank. Examples of the mechanical agitation typemixer include a high-speed agitation type mixer and a double arm typemixer, and a high-speed agitation type mixer is preferably used from theviewpoint of increasing the homogeneity of raw materials in the mixtureof the raw material inclusion and the complexing agent and obtaining notonly predetermined average particle diameter and specific surface areabut also a high ionic conductivity. In addition, examples of thehigh-speed agitation type mixer include a vertical axis rotating typemixer and a lateral axis rotating type mixer, and mixers of any of thesetypes may be used.

Examples of a shape of the impeller which is used in the mechanicalagitation type mixer include a blade type, an arm type, a ribbon type, amultistage blade type, a double arm type, a shovel type, a twin-shaftblade type, a flat blade type, and a C type blade type. From theviewpoint of increasing the homogeneity of raw materials in the rawmaterial inclusion and obtaining not only predetermined average particlediameter and specific surface area but also a high ionic conductivity, ashovel type, a flat blade type, a C type blade type, and the like arepreferred.

A temperature condition on the occasion of mixing the raw materialinclusion and the complexing agent is not particularly limited, and forexample, it is −30 to 100° C., preferably −10 to 50° C., and morepreferably around room temperature (23° C.) (for example, (roomtemperature) about 5° C.). In addition, a mixing time is about 0.1 to150 hours, and from the viewpoint of more uniformly mixing the rawmaterial inclusion and the complexing agent, thereby obtaining not onlypredetermined average particle diameter and specific surface area butalso a high ionic conductivity, the mixing time is preferably 1 to 120hours, more preferably 4 to 100 hours, and still more preferably 8 to 80hours.

By mixing the raw material inclusion and the complexing agent, owing toan action of the lithium element, the sulfur element, the phosphoruselement, and the halogen element, all of which are contained in the rawmaterials, with the complexing agent, an electrolyte precursor in whichthese elements are bound directly with each other via and/or not via thecomplexing agent is obtained. That is, in the present production method,the electrolyte precursor obtained through mixing of the raw materialinclusion and the complexing agent is constituted of the complexingagent, the lithium element, the sulfur element, the phosphorus element,and the halogen element, and by mixing the raw material inclusion andthe complexing agent, a material containing the electrolyte precursor(hereinafter sometimes referred to as “electrolyte precursor inclusion”)is obtained. In the present embodiment, the resulting electrolyteprecursor is not one completely dissolved in the complexing agent thatis a liquid, and typically, a suspension containing the electrolyteprecursor that is a solid is obtained. In consequence, the presentproduction method is corresponding to a heterogeneous system in aso-called liquid-phase method.

(Pulverization)

The present production method preferably includes pulverization of theelectrolyte precursor. By pulverizing the electrolyte precursor, a solidelectrolyte having a small particle diameter is obtained. In addition,the reduction of the ionic conductivity can be suppressed.

The pulverization of the electrolyte precursor is different frommechanical milling that is a so-called solid-phase method and is not onefor obtaining an amorphous or crystalline solid electrolyte owing to amechanical stress. As mentioned above, the electrolyte precursorcontains the complexing agent, and the lithium-containing structure,such as a PS₄ structure, and the raw materials containing lithium, suchas a lithium halide, are bound (coordinated) with each other via thecomplexing agent. Then, it may be considered that when the electrolyteprecursor is pulverized, fine particles of the electrolyte precursor areobtained while maintaining the aforementioned binding (coordination) anddispersing state. By subjecting this electrolyte precursor to heating asmentioned later, the components bound (coordinated) via the complexingagent are linked with each other at the same time of removal of thecomplexing agent, and the reaction with the crystalline sulfide solidelectrolyte easily takes place. For that reason, growth of largeparticles owing to aggregation of particles with each other as seen inusual synthesis of a solid electrolyte is hardly generated, andatomization can be readily achieved.

The pulverizer which is used for pulverization of the electrolyteprecursor is not particularly restricted so long as it is able topulverize the particles, and for example, a medium type pulverizer usinga pulverization medium can be used. Among medium type pulverizers,taking into account the fact that the electrolyte precursor is in aliquid state or slurry state mainly accompanied by liquids, such as thecomplexing agent and the solvent, a wet-type pulverizer capable ofcoping with wet pulverization is preferred.

Representative examples of the wet-type pulverizer include a wet-typebead mill, a wet-type ball mill, and a wet-type vibration mill, and awet-type bead mill using beads as a pulverization medium is preferredfrom the standpoint that it is able to freely adjust the condition of apulverization operation and is easy to cope with materials having asmaller particle diameter. In addition, a dry-type pulverizer, such as adry-type medium type pulverizer, e.g., a dry-type bead mill, a dry-typeball mill, and a dry-type vibration mill, and a dry-type non-mediumpulverizer, e.g., a jet mill, can also be used.

The electrolyte precursor to be pulverized by the pulverizer istypically fed as the electrolyte precursor inclusion which is obtainedby mixing the raw material inclusion and the complexing agent and mainlyfed in a liquid state or slurry state. That is, an object to bepulverized by the pulverizer mainly becomes an electrolyte precursorinclusion liquid or an electrolyte precursor-containing slurry.Accordingly, the pulverizer which is used in the present embodiment ispreferably a flow type pulverizer capable of being optionally subjectedto circulation driving of the electrolyte precursor inclusion liquid orelectrolyte precursor-containing slurry. More specifically, it ispreferred to use a pulverizer of a mode of circulating the electrolyteprecursor inclusion liquid or electrolyte precursor-containing slurrybetween a pulverizer (pulverization mixer) of pulverizing the slurry anda temperature-holding tank (reactor) as disclosed in JP 2010-140893 A.

The size of the bead which is used for the pulverizer may beappropriately selected according to the desired particle diameter andtreatment amount and the like, and for example, it may be about 0.05 mmφor more and 5.0 mmφ or less, and it is preferably 0.1 mmφ or more and3.0 mmφ or less, and more preferably 0.3 mmφ or more and 1.5 mmφ or lessin terms of a diameter of the bead.

As the pulverizer which is used for pulverization of the electrolyteprecursor, a machine capable of pulverizing an object using ultrasonicwaves, for example, a machine called an ultrasonic pulverizer, anultrasonic homogenizer, a probe ultrasonic pulverizer, or the like, canbe used.

In this case, various conditions, such as a frequency of ultrasonicwaves, may be appropriately selected according to the desired averageparticle diameter of the electrolyte precursor, and the like. Thefrequency may be, for example, about 1 kHz or more and 100 kHz or less,and from the viewpoint of more efficiently pulverizing the electrolyteprecursor, it is preferably 3 kHz or more and 50 kHz or less, morepreferably 5 kHz or more and 40 kHz or less, and still more preferably10 kHz or more and 30 kHz or less.

An output which the ultrasonic pulverizer has may be typically about 500to 16,000 W, and it is preferably 600 to 10,000 W, more preferably 750to 5,000 W, and still more preferably 900 to 1,500 W.

Although an average particle diameter (D₅₀) of the electrolyte precursorwhich is obtained through pulverization is appropriately determinedaccording to the desire, it is typically 0.01 μm or more and 50 μm orless, preferably 0.03 μm or more and 5 μm or less, more preferably 0.05μm or more and 3 μm or less. By taking such an average particlediameter, it becomes possible to cope with the desire of the solidelectrolyte having a small particle diameter as 1 μm or less in terms ofan average particle diameter.

A time for pulverization is not particularly restricted so long as it isa time such that the electrolyte precursor has the desired averageparticle diameter, and it is typically 0.1 hours or more and 100 hoursor less. From the viewpoint of efficiently regulating the particlediameter to the desired size, the time for pulverization is preferably0.3 hours or more and 72 hours or less, more preferably 0.5 hours ormore and 48 hours or less, and still more preferably 1 hour or more and24 hours or less.

The pulverization may be performed after drying the electrolyteprecursor inclusion, such as the electrolyte precursor inclusion liquidor electrolyte precursor-containing slurry, to form the electrolyteprecursor as a powder.

In this case, among the aforementioned pulverizers as exemplified as thepulverizer which may be used in the present production method, any oneof the dry-type pulverizers is preferably used. Besides, the itemsregarding the pulverization, such as a pulverization condition, are thesame as those in the pulverization of the electrolyte precursorinclusion liquid or electrolyte precursor-containing slurry, and theaverage particle diameter of the electrolyte precursor obtained throughpulverization is also the same as that as mentioned above.

(Drying)

The present production method may include drying of the electrolyteprecursor inclusion (typically, suspension). According to this, a powderof the electrolyte precursor is obtained. By performing drying inadvance, it becomes possible to efficiently perform heating. The dryingand the subsequent heating may be performed in the same process.

The electrolyte precursor inclusion can be dried at a temperatureaccording to the kind of the remaining complexing agent (complexingagent not incorporated into the electrolyte precursor). For example, thedrying can be performed at a temperature of a boiling point of thecomplexing agent or higher. In addition, the drying can be performedthrough drying under reduced pressure (vacuum drying) by using a vacuumpump or the like at typically 5 to 100° C., preferably 10 to 85° C.,more preferably 15 to 70° C., and still more preferably around roomtemperature (23° C.) (for example, (room temperature) about 5° C.), tovolatilize the complexing agent.

The drying may be performed by subjecting the electrolyte precursorinclusion to solid-liquid separation by means of filtration with a glassfilter or the like, or decantation, or solid-liquid separation with acentrifuge or the like. In the present embodiment, after performing thesolid-liquid separation, the drying may be performed under theaforementioned temperature condition.

Specifically, for the solid-liquid separation, decantation in which theelectrolyte precursor inclusion is transferred into a container, andafter the electrolyte precursor is precipitated, the complexing agentand solvent as a supernatant are removed, or filtration with a glassfilter having a pore size of, for example, about 10 to 200 μm, andpreferably 20 to 150 μm, is easy.

The electrolyte precursor has such a characteristic feature that it isconstituted of the complexing agent, the lithium element, the sulfurelement, the phosphorus element, and the halogen element, and in theX-ray diffraction pattern in the X-ray diffractometry, peaks differentfrom the peaks derived from the raw materials are observed, and itpreferably contains a co-crystal constituted of the complexing agent,the lithium element, the sulfur element, the phosphorus element, and thehalogen element. When only the raw material inclusion is merely mixed,the peaks derived from the raw materials are merely observed, whereaswhen the raw material inclusion and the complexing agent are mixed,peaks different from the peaks derived from the raw materials areobserved. Thus, the electrolyte precursor (co-crystal) has a structureexplicitly different from the raw materials themselves contained in theraw material inclusion. This matter is specifically confirmed in thesection of Examples. Measurement examples of the X-ray diffractionpatterns of the electrolyte precursor (co-crystal) and the respectiveraw materials, such as lithium sulfide, are shown in FIGS. 3 and 4,respectively. It is noted from the X-ray diffraction patterns that theelectrolyte precursor (co-crystal) has a predetermined crystalstructure. In addition, the diffraction pattern of the electrolyteprecursor does not contain the diffraction patterns of any rawmaterials, such as lithium sulfide, as shown in FIG. 4, and thus, it isnoted that the electrolyte precursor (co-crystal) has a crystalstructure different from the raw materials.

In addition, the electrolyte precursor (co-crystal) has such acharacteristic feature that it has a structure different from thecrystalline solid electrolyte. This matter is also specificallyconfirmed in the section of Examples. The X-ray diffraction pattern ofthe crystalline solid electrolyte is also shown in FIG. 4, and it isnoted that the foregoing diffraction pattern is different from thediffraction pattern of the electrolyte precursor (co-crystal). Theelectrolyte precursor (co-crystal) has the predetermined crystalstructure and is also different from the amorphous solid electrolytehaving a broad pattern as shown in FIG. 4.

The co-crystal is constituted of the complexing agent, the lithiumelement, the sulfur element, the phosphorus element, and the halogenelement, and typically, it may be presumed that a complex structure inwhich the lithium element and the other elements are bound directly witheach other via and/or not via the complexing agent is formed.

Here, the fact that the complexing agent constitutes the co-crystal canbe, for example, confirmed through gas chromatography analysis.Specifically, the complexing agent contained in the co-crystal can bequantitated by dissolving a powder of the electrolyte precursor inmethanol and subjecting the obtained methanol solution to gaschromatography analysis.

Although the content of the complexing agent in the electrolyteprecursor varies with the molecular weight of the complexing agent, itis typically about 10% by mass or more and 70% by mass or less, andpreferably 15% by mass or more and 65% by mass or less.

In the present production method, what the co-crystal containing thehalogen element is formed is preferred from the standpoint of enhancingnot only predetermined average particle diameter and specific surfacearea but also a high ionic conductivity. By using the complexing agent,the lithium-containing structure, such as a PS₄ structure, and thelithium-containing raw materials, such as a lithium halide, are bound(coordinated) with each other via the complexing agent, the co-crystalin which the halogen element is more likely dispersed and fixed isreadily obtained, and not only the predetermined average particlediameter and specific surface area but also the ionic conductivity isenhanced.

The matter that the halogen element in the electrolyte precursorconstitutes the co-crystal can be confirmed from the fact that even whenthe solid-liquid separation of the electrolyte precursor inclusion isperformed, the predetermined amount of the halogen element is containedin the electrolyte precursor. This is because the halogen element whichdoes not constitute the co-crystal is easily eluted as compared with thehalogen element constituting the co-crystal and discharged into theliquid of solid-liquid separation. In addition, the foregoing matter canalso be confirmed from the fact that by performing composition analysisthrough ICP analysis (inductively coupled plasma atomic emissionspectrophotometry) of the electrolyte precursor or solid electrolyte, aproportion of the halogen element in the electrolyte precursor or solidelectrolyte is not remarkably lowered as compared with a proportion ofthe halogen element fed from the raw materials.

The amount of the halogen element remaining in the electrolyte precursoris preferably 30% by mass or more, more preferably 35% by mass or more,and still more preferably 40% by mass or more relative to the chargedcomposition. An upper limit of the amount of the halogen elementremaining in the electrolyte precursor is 100% by mass.

(Heating)

It is preferred that the present production method includes heating ofthe electrolyte precursor to obtain the amorphous solid electrolyte; andheating of the electrolyte precursor or amorphous solid electrolyte toobtain the crystalline solid electrolyte. In view of the fact thatheating of the electrolyte precursor is included, the complexing agentin the electrolyte precursor is removed, and the amorphous solidelectrolyte and the crystalline solid electrolyte each containing thelithium element, the sulfur element, the phosphorus element, and thehalogen element are obtained. In addition, the electrolyte precursor tobe heated by the present heating may be an electrolyte precursorpulverized product which has been pulverized through the aforementionedpulverization.

Here, the fact that the complexing agent in the electrolyte precursor isremoved is supported by the facts that in addition to the fact that itis evident from the results of the X-ray diffraction pattern, the gaschromatography analysis, and the like that the complexing agentconstitutes the co-crystal of the electrolyte precursor, the solidelectrolyte obtained by removing the complexing agent through heating ofthe electrolyte precursor is identical in the X-ray diffraction patternwith the solid electrolyte obtained by the conventional method withoutusing the complexing agent.

In the present production method, the solid electrolyte is obtained byheating the electrolyte precursor to remove the complexing agent in theelectrolyte precursor, and it is preferred that the content of thecomplexing agent in the solid electrolyte is low as far as possible.However, the complexing agent may be contained to an extent that theperformance of the solid electrolyte is not impaired. The content of thecomplexing agent in the solid electrolyte may be typically 10% by massor less, and it is preferably 5% by mass or less, more preferably 3% bymass or less, and still more preferably 1% by mass or less.

In the present production method, in order to obtain the crystallinesolid electrolyte, it may be obtained by heating the electrolyteprecursor, or it may be obtained by heating the electrolyte precursor toobtain the amorphous solid electrolyte and then heating the amorphoussolid electrolyte. That is, in the present production method, theamorphous solid electrolyte can also be produced. Conventionally, inorder to obtain a crystalline solid electrolyte having a high ionicconductivity, for example, a solid electrolyte having a thio-LISICONRegion II-type crystal structure as mentioned later, it was requiredthat an amorphous solid electrolyte is prepared through mechanicalpulverization treatment, such as mechanical milling, or other meltquenching treatment or the like, and then, the amorphous solidelectrolyte is heated. But, it may be said that the present productionmethod is superior to the conventional production method by mechanicalmilling treatment or the like from the standpoint that a crystallinesolid electrolyte having a thio-LISICON Region II-type crystal structureis obtained even by a method of not performing mechanical pulverizationtreatment, other melt quenching treatment, or the like.

In the present production method, whether or not the amorphous solidelectrolyte is obtained, whether or not the crystalline solidelectrolyte is obtained, whether or not after obtaining the amorphoussolid electrolyte, the crystalline solid electrolyte is obtained, orwhether or not the crystalline solid electrolyte is obtained directlyfrom the electrolyte precursor is appropriately selected according tothe desire, and is able to be adjusted by the heating temperature, theheating time, or the like.

For example, in the case of obtaining the amorphous solid electrolyte,the heating temperature of the electrolyte precursor may be determinedaccording to the structure of the crystalline solid electrolyte which isobtained by heating the amorphous solid electrolyte (or the electrolyteprecursor). Specifically, the heating temperature may be determined bysubjecting the amorphous solid electrolyte (or the electrolyteprecursor) to differential thermal analysis (DTA) with a differentialthermal analysis device (DTA device) under a temperature rise conditionof 10° C./min and adjusting the temperature to a range of preferably 5°C. or lower, more preferably 10° C. or lower, and still more preferably20° C. or lower starting from a peak top temperature of the exothermicpeak detected on the lowermost temperature side. Although a lower limitthereof is not particularly restricted, it may be set to a temperatureof about [(peak top temperature of the exothermic peak detected on thelowermost temperature side)−40° C.] or higher. By regulating the heatingtemperature to such a temperature range, the amorphous solid electrolyteis obtained more efficiently and surely. Although the heatingtemperature for obtaining the amorphous solid electrolyte cannot beunequivocally prescribed because it varies with the structure of theresulting crystalline solid electrolyte, in general, it is preferably135° C. or lower, more preferably 130° C. or lower, and still morepreferably 125° C. or lower. Although a lower limit of the heatingtemperature is not particularly limited, it is preferably 90° C. orhigher, more preferably 100° C. or higher, and still more preferably110° C. or higher.

In the case of obtaining the crystalline solid electrolyte by heatingthe amorphous solid electrolyte or directly from the electrolyteprecursor, the heating temperature may be determined according to thestructure of the crystalline solid electrolyte, and it is preferablyhigher than the aforementioned heating temperature for obtaining theamorphous solid electrolyte. Specifically, the heating temperature maybe determined by subjecting the amorphous solid electrolyte (or theelectrolyte precursor) to differential thermal analysis (DTA) with adifferential thermal analysis device (DTA device) under a temperaturerise condition of 10° C./min and adjusting the temperature to a range ofpreferably 5° C. or higher, more preferably 10° C. or higher, and stillmore preferably 20° C. or higher starting from a peak top temperature ofthe exothermic peak detected on the lowermost temperature side. Althoughan upper limit thereof is not particularly restricted, it may be set toa temperature of about [(peak top temperature of the exothermic peakdetected on the lowermost temperature side+40° C.] or lower. Byregulating the heating temperature to such a temperature range, thecrystalline solid electrolyte is obtained more efficiently and surely.Although the heating temperature for obtaining the crystalline solidelectrolyte cannot be unequivocally prescribed because it varies withthe structure of the resulting crystalline solid electrolyte, ingeneral, it is preferably 130° C. or higher, more preferably 135° C. orhigher, and still more preferably 140° C. or lower. Although an upperlimit of the heating temperature is not particularly limited, it ispreferably 300° C. or lower, more preferably 280° C. or lower, and stillmore preferably 250° C. or lower.

Although the heating time is not particularly limited so long as it is atime for which the desired amorphous solid electrolyte or crystallinesolid electrolyte is obtained, for example, it is preferably 1 minute ormore, more preferably 10 minutes or more, still more preferably 30minutes or more, and yet still more preferably 1 hour or more. Inaddition, though an upper limit of the heating temperature is notparticularly restricted, it is preferably 24 hours or less, morepreferably 10 hours or less, still more preferably 5 hours or less, andyet still more preferably 3 hours or less.

It is preferred that the heating is performed in an inert gas atmosphere(for example, a nitrogen atmosphere and an argon atmosphere) or in areduced pressure atmosphere (especially, in vacuo). This is becausedeterioration (for example, oxidation) of the crystalline solidelectrolyte can be prevented from occurring. Although a method forheating is not particularly limited, for example, a method of using ahot plate, a vacuum heating device, an argon gas atmosphere furnace, ora firing furnace can be adopted. In addition, industrially, a lateraldryer or a lateral vibration fluid dryer provided with a heating meansand a feed mechanism, or the like may be selected according to theheating treatment amount.

(Amorphous Solid Electrolyte)

The amorphous solid electrolyte which is obtained by the presentproduction method contains the lithium element, the sulfur element, thephosphorus element, and the halogen element. As representative examplesthereof, there are preferably exemplified solid electrolytes constitutedof lithium sulfide, phosphorus sulfide, and a lithium halide, such asLi₂S—P₂S₅—LiI, Li₂S—P₂S₅—LiCl, Li₂S—P₂S₅—LiBr, and Li₂S—P₂S₅—LiI—LiBr;and solid electrolytes further containing other element, such as anoxygen element and a silicon element, for example, Li₂S—P₂S₅—Li₂O—LiIand Li₂S—SiS₂—P₂S₅—LiI. From the viewpoint of obtaining a higher ionicconductivity, solid electrolytes constituted of lithium sulfide,phosphorus sulfide, and a lithium halide, such as Li₂S—P₂S₅—LiI,Li₂S—P₂S₅—LiCl, Li₂S—P₂S₅—LiBr, and Li₂S—P₂S₅—LiI—LiBr, are preferred.The kinds of the elements constituting the amorphous solid electrolytecan be confirmed by, for example, an inductivity coupled plasma opticalemission spectrometer (ICP).

In the case where the amorphous solid electrolyte obtained in thepresent production method is one having at least Li₂S—P₂S₅, from theviewpoint of obtaining a higher ionic conductivity, a molar ratio ofLi₂S to P₂S₅ is preferably (65 to 85)/(15 to 35), more preferably (70 to80)/(20 to 30), and still more preferably (72 to 78)/(22 to 28).

In the case where the amorphous solid electrolyte obtained in thepresent production method is Li₂S—P₂S₅—LiI—LiBr, the total content oflithium sulfide and phosphorus pentasulfide is preferably 60 to 95 mol%, more preferably 65 to 90 mol %, and still more preferably 70 to 85mol %. In addition, a proportion of lithium bromide relative to thetotal of lithium bromide and lithium iodide is preferably 1 to 99 mol %,more preferably 20 to 90 mol %, still more preferably 40 to 80 mol %,and especially preferably 50 to 70 mol %.

In the amorphous solid electrolyte obtained in the present productionmethod, a blending ratio (molar ratio) of lithium element to sulfurelement to phosphorous element to halogen atom is preferably (1.0 to1.8)/(1.0 to 2.0)/(0.1 to 0.8)/(0.01 to 0.6), more preferably (1.1 to1.7)/(1.2 to 1.8)/(0.2 to 0.6)/(0.05 to 0.5), and still more preferably(1.2 to 1.6)/(1.3 to 1.7)/(0.25 to 0.5)/(0.08 to 0.4). In addition, inthe case of using a combination of bromine and iodine as the halogenelement, a blending ratio (molar ratio) of lithium element to sulfurelement to phosphorus element to bromine to iodine is preferably (1.0 to1.8)/(1.0 to 2.0)/(0.1 to 0.8)/(0.01 to 3.0)/(0.01 to 0.3), morepreferably (1.1 to 1.7)/(1.2 to 1.8)/(0.2 to 0.6)/(0.02 to 0.25)/(0.02to 0.25), still more preferably (1.2 to 1.6)/(1.3 to 1.7)/(0.25 to0.5)/(0.03 to 0.2)/(0.03 to 0.2), and yet still more preferably (1.35 to1.45)/(1.4 to 1.7)/(0.3 to 0.45)/(0.04 to 0.18)/(0.04 to 0.18). Byallowing the blending ratio (molar ratio) of lithium element to sulfurelement to phosphorus element to halogen element to fall within theaforementioned range, it becomes easy to provide a solid electrolytehaving a thio-LISICON Region II-type crystal structure as mentionedlater and having a higher ionic conductivity.

Although the shape of the amorphous solid electrolyte is notparticularly restricted, examples thereof include a granular shape. Theaverage particle diameter (D₅₀) of the granular amorphous solidelectrolyte is, for example, within a range of 0.01 to 500 μm, and 0.1to 200 μm.

A volume-based average particle diameter of the amorphous solidelectrolyte obtained by the present production method is 3 μm or more, avalue of which is the same as the average particle diameter of thesulfide solid electrolyte of the present embodiment as mentioned above.

A specific surface area measured by the BET method of the amorphoussolid electrolyte obtained by the present production method is 20 m²/gor more, a value of which is the same as the specific surface area ofthe sulfide solid electrolyte of the present embodiment as mentionedabove.

(Crystalline Solid Electrolyte)

The crystalline solid electrolyte obtained by the present productionmethod may be a so-called glass ceramics which is obtained by heatingthe amorphous solid electrolyte to a crystallization temperature orhigher. Examples of a crystal structure thereof include an Li₃PS₄crystal structure, an Li₄P₂S₆ crystal structure, an Li₇PS₆ crystalstructure, an Li₇P₃S₁₁ crystal structure, and a crystal structure havingpeaks at around of 2θ=20.2° and 23.6° (see, for example, JP 2013-16423A).

In addition, examples thereof include an Li_(4−x)Ge_(1−x)P_(x)S₄-basedthio-LISICON Region II-type crystal structure (see Kanno, et al.,Journal of The Electrochemical Society, 148 (7) A742-746 (2001)) and acrystal structure similar to the Li_(4−x)Ge_(1−x)P_(x)S₄-basedthio-LISICON Region II-type crystal structure (see Solid State Ionics,177 (2006), 2721-2725). Among them, the thio-LISICON Region II-typecrystal structure is preferred as the crystal structure of thecrystalline solid electrolyte obtained by the present production methodfrom the standpoint that a higher ionic conductivity is obtained. Here,the “thio-LISICON Region II-type crystal structure” expresses any one ofan Li_(4−x)Ge_(1−x)P_(x)S₄-based thio-LISICON Region II-type crystalstructure and a crystal structure similar to theLi_(4−x)Ge_(1−x)P_(x)S₄-based thio-LISICON Region II-type crystalstructure. In addition, though the crystalline solid electrolyteobtained by the present production method may be one having theaforementioned thio-LISICON Region II-type crystal structure or may beone having the thio-LISICON Region II-type crystal structure as a maincrystal, it is preferably one having the thio-LISICON Region II-typecrystal structure as a main crystal from the viewpoint of obtaining ahigher ionic conductivity. In this specification, the wording “having asa main crystal” means that a proportion of the crystal structure servingas an object in the crystal structure is 80% or more, and it ispreferably 90% or more, and more preferably 95% or more. In addition,from the viewpoint of obtaining a higher ionic conductivity, thecrystalline solid electrolyte obtained by the present production methodis preferably one not containing crystalline Li₃PS₄ (β-Li₃PS₄).

In the X-ray diffractometry using a CuKα ray, the Li₃PS₁ crystalstructure gives diffraction peaks, for example, at around 2θ=17.5°,18.3°, 26.1°, 27.3°, and 30.0; the Li₄P₂S₆ crystal structure givesdiffraction peaks, for example, at around 2θ=16.9°, 27.1°, and 32.5°;the Li₇PS₆ crystal structure gives diffraction peaks, for example, ataround 2θ=15.3°, 25.2°, 29.6°, and 31.0°; the Li₇P₃S₁₁ crystal structuregives diffraction peaks, for example, at around a2θ=17.8°, 18.5°, 19.7°,21.8°, 23.7°, 25.9°, 29.6°, and 30.0°; the Li_(4−x)Ge_(1−x)P_(x)S₄-basedthio-LISICON Region II-type crystal structure gives diffraction peaks,for example, at around 2θ=20.1°, 23.9°, and 29.5°; and the crystalstructure similar to the Li_(4−x)Ge_(1−x)P_(x)S₄-based thio-LISICONRegion II-type crystal structure gives diffraction peaks, for example,at around 2θ=20.2° and 23.6°. The position of these peaks may varywithin a range of ±0.5°.

As mentioned above, in the case when the thio-LISICON Region II-typecrystal structure is obtained in the present embodiment, the foregoingcrystal structure is preferably one not containing crystalline Li₃PS₄(β-Li₃PS₄). FIG. 3 shows an X-ray diffractometry example of thecrystalline solid electrolyte obtained by the present production method.In addition, FIG. 4 shows an X-ray diffractometry example of crystallineLi₃PS₄ (β-Li₃PS₄). As grasped from FIGS. 3 and 4, the sulfide solidelectrolyte of the present embodiment does not have diffraction patternsat 2θ=17.5° and 26.1°, or even in the case where it has diffractionpatterns, extremely small peaks as compared with the diffraction peaksof the thio-LISICON Region II-type crystal structure are merelydetected.

The crystal structure represented by a compositional formulaLi_(7−x)P_(1−y)Si_(y)S₆ or Li_(7+x)P_(1−y)Si_(y)S₆ (x is −0.6 to 0.6,and y is 0.1 to 0.6), which has the aforementioned structure skeleton ofLi₇PS₆ and in which a part of P is substituted with Si, is a cubiccrystal or a rhombic crystal, and is preferably a cubic crystal, and inX-ray diffractometry using a CuKα ray, the crystal structure gives peaksappearing mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°,and 52.0°. The crystal structure represented by the aforementionedcompositional formula Li_(7−x−2y)PS_(6−x−y−1)Cl_(x) (0.8≤x≤1.7, and0<y≤(−0.25+0.05)) is preferably a cubic crystal, and in the X-raydiffractometry using a CuKα ray, the crystal structure gives peaksappearing mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°,and 52.0°. In addition, the crystal structure represented by theaforementioned compositional formula Li_(7−x)PS_(6−x)Ha_(x) (Harepresents Cl or Br, and x is preferably 0.2 to 1.8) is preferably acubic crystal, and in the X-ray diffractometry using a CuKα ray, thecrystal structure gives peaks appearing mainly at 2θ=15.5°, 18.0°,25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°.

These peak positions may vary within a range of ±0.5.

Further, in the crystalline sulfide solid electrolyte obtained by thepresent production method, a half width of a maximum peak including thebackground at 2θ=10 to 40° in the X-ray diffractometry using a CuKα rayis preferably Δ2θ=0.32 or less. In view of the fact that the crystallinesulfide solid electrolyte has such properties, a higher ionicconductivity is obtained, and the battery performance is enhanced. Fromthe same viewpoint, the half width of a maximum peak is more preferablyΔ2θ=0.30 or less, and still more preferably Δ2θ=0.28 or less.

As the crystalline sulfide solid electrolyte having such properties,there is typically exemplified one having a thio-LISICON Region II-typecrystal structure.

For example, FIG. 5 shows an X-ray diffractometry example of acrystalline sulfide solid electrolyte having a thio-LISICON RegionII-type crystal structure obtained in Example 1, a maximum peakincluding the background at 2θ=10 to 40° is a peak at 20.1°, and thus,it is noted that the half width in the foregoing peak has a sharp peakas Δ2θ=0.25. In this way, in view of the fact that the maximum peak hasa sharp peak whose half width is 0.32 or less, the crystalline sulfidesolid electrolyte reveals an extremely high ionic conductivity, and thebattery performance can be enhanced. The matter that the crystallinesulfide solid electrolyte has such a half width expresses highcrystallinity. According to this, disintegration can be achieved with asmall energy, and therefore, a lowering of the ionic conductivity owingto vitrification (amorphization) hardly takes places. In addition, theprecursor for mechanical treatment of the present embodiment hasfavorable crystallinity while having a porous structure having arelatively large specific surface area. Thus, even when a part or thewhole of the precursor for mechanical treatment is vitrified owing todisintegration and granulation, a change of the morphology duringrecrystallization is relatively suppressed, and therefore, themorphology can be readily adjusted by the mechanical treatment.

The calculation of the half width can be determined in the followingmanner.

A range of [(maximum peak)±2°] is used. When defining a proportion ofthe Lorentzian function as A (0≤A≤1), a peak intensity correction valueas B, a 2θ maximum peak as C, a peak position of a range to be used forcalculation (C±2°) as D, a half value as E, a background as F, and eachpeak intensity of a peak range to be used for calculation as G,respectively, the following calculation is performed at every peakposition on defining the variables as A, B, C, D, E, and F.

H=G−{B×{A/(1+(D−C)² /E ²)+(1−A)×exp(−1×(D−C)² /E ²)}+F}

H's are totaled within the peak (C±2°), and the total value is minimizedwith the Solver function of a spreadsheet program Excel (MicrosoftCorporation) in terms of GRG nonlinearity, whereby the half width can bedetermined.

Although the shape of the crystalline solid electrolyte is notparticularly restricted, examples thereof include a granular shape. Theaverage particle diameter (D₅₀) of the granular amorphous solidelectrolyte is, for example, within a range of 0.01 to 500 μm, and 0.1to 200 μm.

A volume-based average particle diameter of the crystalline solidelectrolyte obtained by the present production method is 3 μm or more, avalue of which is the same as the average particle diameter of thesulfide solid electrolyte of the present embodiment as mentioned above.

In addition, a specific surface area measured by the BET method of thecrystalline solid electrolyte obtained by the present production methodis 20 m²/g or more, a value of which is the same as the specific surfacearea of the sulfide solid electrolyte of the present embodiment asmentioned above.

Embodiment B

Next, the Embodiment B is described.

The Embodiment B is concerned with a mode in which in the presentproduction method including mixing a raw material inclusion containing alithium element, a sulfur element, a phosphorus element, and a halogenelement with a complexing agent, raw materials containing, as the rawmaterial inclusion, a solid electrolyte, such as Li₃PS₄, and the likeand the complexing agent are used. In the Embodiment A, the electrolyteprecursor is formed while synthesizing the lithium-containing structure,such as Li₃PS₄, existent as a main structure in the solid electrolyteobtained by the present production method, through reaction among theraw materials, such as lithium sulfide, and therefore, it may beconsidered that a constitution ratio of the aforementioned structure isliable to become small.

Then, in the Embodiment B, a solid electrolyte containing theaforementioned structure is previously prepared by means of productionor the like, and this is used as the raw material. According to this, anelectrolyte precursor in which the aforementioned structure and the rawmaterials containing lithium, such the lithium halide, are bound(coordinated) with each other via the complexing agent, and the halogenelement is dispersed and fixed is more likely obtained. As a result, asolid electrolyte having not only predetermined average particlediameter and specific surface area but also a high ionic conductivity,in which the generation of hydrogen sulfide is suppressed, is obtained.

Examples of the raw material containing a lithium element, a sulfurelement, and a phosphorus element, which may be used in the EmbodimentB, include an amorphous solid electrolyte or crystalline solidelectrolyte having a PS₄ structure as a molecular structure. From theviewpoint of suppressing the generation of hydrogen sulfide, a P₂S₇structure-free amorphous solid electrolyte or crystalline solidelectrolyte is preferred. As such a solid electrolyte, ones produced bya conventionally existing production method, such as a mechanicalmilling method, a slurry method, and a melt quenching method, can beused, and commercially available products can also be used.

In addition, in this case, the solid electrolyte containing a lithiumelement, a sulfur element, and a phosphorus element is preferably anamorphous solid electrolyte. The dispersibility of the halogen elementin the electrolyte precursor is enhanced, and the halogen element iseasily bound with the lithium element, the sulfur element, and thephosphorus element in the solid electrolyte, and as a result, a solidelectrolyte having not only predetermined average particle diameter andspecific surface area but also a higher ionic conductivity can beobtained.

In the embodiment B, the content of the amorphous solid electrolytehaving a PS₄ structure or the like is preferably 60 to 100 mol %, morepreferably 65 to 90 mol %, and still more preferably 70 to 80 mol %relative to the total of the raw materials.

In the case of using the amorphous solid electrolyte having a PS₄structure or the like and the halogen simple substance, the content ofthe halogen simple substance is preferably 1 to 50 mol %, morepreferably 2 to 40 mol %, still more preferably 3 to 25 mol %, and yetstill more preferably 3 to 15 mol % relative to the amorphous solidelectrolyte having a PS₄ structure or the like.

Besides, in the case of using the halogen simple substance and thelithium halide and the case of using the two halogen simple substances,the same as in the Embodiment A is applicable.

In the Embodiment B, in all other cases than the raw materials, forexample, the complexing agent, the mixing, the heating, the drying, theamorphous solid electrolyte, and the crystalline solid electrolyte, andthe like are the same as those described in the Embodiment A.

In addition, in the Embodiment B, the matter that what the electrolyteprecursor is pulverized is preferred, the pulverizer to be used forpulverization, the matter that after mixing or after drying, thepulverization may be performed, various conditions regardingpulverization, and so on are also the same as those in the Embodiment A.

Embodiments C and D

As shown in the flow chart of FIG. 2, the Embodiments C and D aredifferent from the Embodiments A and B, respectively from the standpointthat a solvent is added to the raw material inclusion and the complexingagent. The Embodiments C and D are concerned with a heterogeneous methodof solid-liquid coexistence, whereas in the Embodiments A and B, theelectrolyte precursor that is a solid is formed in the complexing agentthat is a liquid. At this time, when the electrolyte precursor is easilysoluble in the complexing agent, there is a case where separation of thecomponents is generated. In the Embodiments C and D, by using a solventin which the electrolyte precursor is insoluble, elution of thecomponents in the electrolyte precursor can be suppressed.

(Solvent)

In the production method of the Embodiments C and D, it is preferred toadd the solvent to the raw material inclusion and the complexing agent.In view of the fact that the raw material inclusion and the complexingagent are mixed using the solvent, an effect to be brought by using thecomplexing agent, namely an effect in which formation of the electrolyteprecursor acting with the lithium element, the sulfur element, thephosphorus element, and the halogen element is promoted, an aggregatevia the lithium-containing structure, such as a PS₄ structure, or thecomplexing agent, and an aggregate via the lithium-containing rawmaterial, such as a lithium halide, or the complexing agent are evenlyexistent, whereby an electrolyte precursor in which the halogen elementis more likely dispersed and fixed is obtained, as a result, not onlypredetermined average particle diameter and specific surface area butalso a high ionic conductivity is obtained, is easily exhibited.

The present production method is a so-called heterogeneous method, andit is preferred that the electrolyte precursor is not completelydissolved in the complexing agent that is a liquid but deposited. In theEmbodiments C and D, by adding the solvent, the solubility of theelectrolyte precursor can be adjusted. In particular, the halogenelement is liable to be eluted from the electrolyte precursor, andtherefore, by adding the solvent, the elution of the halogen element issuppressed, whereby the desired electrolyte precursor is obtained. As aresult, a crystalline solid electrolyte having not only predeterminedaverage particle diameter and specific surface area but also a highionic conductivity, in which the generation of hydrogen sulfide issuppressed, namely the sulfide solid electrolyte of the presentembodiment, can be obtained via the electrolyte precursor in which thecomponents, such as a halogen, are dispersed.

As the solvent having such properties, a solvent having a solubilityparameter of 10 or less is preferably exemplified. In thisspecification, the solubility parameter is described in variousliteratures, for example, “Handbook of Chemistry” (published in 2004,Revised 5th Edition, by Maruzen Publishing Co., Ltd.) and is a value δ((cal/cm³)^(1/2)) calculated according to the following numericalformula (1), which is also called a Hildebrand parameter, SP value.

δ=√{square root over ((ΔH−RT)/V)}  (1)

In the numerical formula (1), ΔH is a molar heating value; R is a gasconstant; T is a temperature; and V is molar volume.

By using the solvent having a solubility parameter of 10 or less, thesolvent has such properties that as compared by the aforementionedcomplexing agent, it relatively hardly dissolves the halogen element,the raw materials containing a halogen element, such as a lithiumhalide, and further the halogen element-containing componentconstituting the co-crystal contained in the electrolyte precursor (forexample, an aggregate in which lithium halide and the complexing agentare bound with each other); it is easy to fix the halogen element withinthe electrolyte precursor; the halogen element is existent in afavorable state in the resulting electrolyte precursor and further thesolid electrolyte; and a solid electrolyte having not only predeterminedaverage particle diameter and specific surface area but also a highionic conductivity is readily obtained. That is, it is preferred thatthe solvent which is used in the present embodiment has such propertiesthat it does not dissolve the electrolyte precursor. From the sameviewpoint, the solubility parameter of the solvent is preferably 9.5 orless, more preferably 9.0 or less, and still more preferably 8.5 orless.

More specifically, as the solvent which is used in the production methodof the Embodiments C and D, it is possible to broadly adopt a solventwhich has hitherto been used in the production of a solid electrolyte.Examples thereof include hydrocarbon solvents, such as an aliphatichydrocarbon solvent, an alicyclic hydrocarbon solvent, and an aromatichydrocarbon solvent; and carbon atom-containing solvents, such as analcohol-based solvent, an ester-based solvent, an aldehyde-basedsolvent, a ketone-based solvent, an ether-based solvent, and a solventcontaining a carbon atom and a hetero atom. Of these, preferably, asolvent having a solubility parameter falling within the aforementionedrange may be appropriately selected and used.

More specifically, examples of the solvent include an aliphatichydrocarbon solvent, such as hexane (7.3), pentane (7.0), 2-ethylhexane,heptane (7.4), octane (7.5), decane, undecane, dodecane, and tridecane;an alicyclic hydrocarbon solvent, such as cyclohexane (8.2) andmethylcyclohexane; an aromatic hydrocarbon solvent, such as benzene,toluene (8.8), xylene (8.8), mesitylene, ethylbenzene (8.8),tert-butylbenzene, trifluoromethylbenzene, nitrobenzene, chlorobenzene(9.5), chlorotoluene (8.8), and bromobenzene; an alcohol-based solvent,such as ethanol (12.7) and butanol (11.4); an ester-based solvent, suchas ethyl acetate (9.1) and butyl acetate (8.5); an aldehyde-basedsolvent, such as formaldehyde, acetaldehyde (10.3), anddimethylformamide (12.1); a ketone-based solvent, such as acetone (9.9)and methyl ethyl ketone; an ether-based solvent, such as diethyl ether(7.4), diisopropyl ether (6.9), dibutyl ether, tetrahydrofuran (9.1),dimethoxyethane (7.3), cycloheptylmethyl ether (8.4), tert-butylmethylether, and anisole; and a solvent containing a carbon atom and a heteroatom, such as acetonitrile (11.9), dimethyl sulfoxide, and carbondisulfide. The numerical values within the parentheses in theaforementioned exemplifications are an SP value.

Of these solvents, an aliphatic hydrocarbon solvent, an alicyclichydrocarbon solvent, an aromatic hydrocarbon solvent, and an ether-basedsolvent are preferred; from the viewpoint of obtaining not onlypredetermined average particle diameter and specific surface area butalso a higher ionic conductivity more stably, heptane, cyclohexane,toluene, ethylbenzene, diethyl ether, diisopropyl ether, dibutyl ether,dimethoxyethane, cycloheptylmethyl ether, tert-butylmethyl ether, andanisole are more preferred; diethyl ether, diisopropyl ether, anddibutyl ether are still more preferred; diisopropyl ether and dibutylether are yet still more preferred; and dibutyl ether is especiallypreferred. The solvent which is used in the present embodiment ispreferably the organic solvent as exemplified above and is an organicsolvent different from the aforementioned complexing agent. In thepresent embodiment, these solvents may be used alone or in combinationof a plural kind thereof.

In the case of using the solvent, the content of the raw materials inthe raw material inclusion may be regulated to one relative to one literof the total amount of the complexing agent and the solvent.

As for drying in the Embodiments C and D, the electrolyte precursorinclusion can be dried at a temperature according to the kind of each ofthe remaining complexing agent (complexing agent not incorporated intothe electrolyte precursor) and the solvent. For example, the drying canbe performed at a temperature of a boiling point of the complexing agentor solvent or higher. In addition, the drying can be performed throughdrying under reduced pressure (vacuum drying) by using a vacuum pump orthe like at typically 5 to 100° C., preferably 10 to 85° C., morepreferably 15 to 70° C., and still more preferably around roomtemperature (23° C.) (for example, (room temperature) about 5° C.), tovolatilize the complexing agent and the solvent. In addition, in theheating in the Embodiments C and D, in the case where the solventremains in the electrolyte precursor, the solvent is also removed.However, different from the complexing agent constituting theelectrolyte precursor, the solvent hardly constitutes the electrolyteprecursor. In consequence, the content of the solvent which may remainin the electrolyte precursor is typically 3% by mass or less, preferably2% by mass or less, and more preferably 1% by mass or less.

In the Embodiment C, in all other cases than the solvent, for example,the complexing agent, the mixing, the heating, the drying, the amorphoussolid electrolyte, and the crystalline solid electrolyte, and the likeare the same as those described in the Embodiment A. In addition, alsoin the Embodiment D, all other cases than the solvent are the same asthose described in the Embodiment B. In addition, in the Embodiments Cand D, the matter that what the electrolyte precursor is pulverized ispreferred, the pulverizer to be used for pulverization, the matter thatafter mixing or after drying, the pulverization may be performed,various conditions regarding pulverization, and so on are also the sameas those in the Embodiment A.

(Application of Sulfide Solid Electrolyte)

The solid electrolyte which is obtained by the present production methodas described above, namely the sulfide solid electrolyte of the presentembodiment, has not only predetermined average particle diameter andspecific surface area but also a high ionic conductivity and also has anexcellent batter performance, and hardly generates hydrogen sulfide, sothat it is suitably used for batteries. In addition, as mentionedpreviously, the foregoing solid electrolyte, i.e., the sulfide solidelectrolyte, is suitably used as a precursor for mechanical treatment,which is used for the mechanical treatment for the purpose of adjustingthe morphology especially by means of mechanical treatment. In the caseof being used as the precursor for mechanical treatment, after formingthe sulfide solid electrolyte having been adjusted to the desiredmorphology, it is suitably used for batteries.

In the case of adopting a lithium element as the conduction species,such is especially suitable. The solid electrolyte of the presentembodiment, which is obtained by the present production method, may beused for a positive electrode layer, may be used for a negativeelectrode layer, or may be used for an electrolyte layer. Each of thelayers can be produced by a known method.

In addition, the aforementioned battery preferably uses a collector inaddition to the positive electrode layer, the electrolyte layer, and thenegative electrode layer, and the collector can be any known one. Forexample, a layer formed by coating Au, Pt, Al, Ti, Cu, or the likecapable of reacting with the aforementioned solid electrolyte, with Auor the like can be used.

[Treatment Method of Sulfide Solid Electrolyte]

The treatment method of a sulfide solid electrolyte of the presentembodiment includes subjecting a sulfide solid electrolyte having avolume-based average particle diameter measured by laser diffractionparticle size distribution measurement of 3 μm or more and a specificsurface area measured by the BET method of 20 m²/g or more to at leastone mechanical treatment selected from disintegration and granulation.That is, the treatment method of a sulfide solid electrolyte of thepresent embodiment includes subjecting the aforementioned sulfide solidelectrolyte (precursor for mechanical treatment) of the presentembodiment to at least one mechanical treatment selected fromdisintegration and granulation.

By subjecting the aforementioned sulfide solid electrolyte (precursorfor mechanical treatment) of the present embodiment to mechanicaltreatment, it is possible to easily adjust the morphology unavailabletraditionally, or adjust a desired morphology, and a sulfide solidelectrolyte having not only desired morphology but also a high ionicconductivity is obtained. In addition, since the precursor formechanical treatment is different from a primary particle in which a newsurface having high activity is exposed through pulverization of acoarse particle, it can be easily atomized through disintegration evenwithout using a dispersant.

Although the method of mechanical treatment of the precursor formechanical treatment is not particularly restricted so long as at leastone treatment of disintegration and granulation is included, examplesthereof include a method of using an apparatus, such as a pulverizer andan agitator.

Examples of the agitator include a mechanical agitation type mixerhaving an impeller provided in a tank, as exemplified as an apparatuswhich may be used for the aforementioned production method of aprecursor for mechanical treatment. Examples of the mechanical agitationtype mixer include a high-speed agitation type mixer and a double armtype mixer, and all of these types can be adopted. From the viewpoint ofmore easily adjusting the desired morphology, a high-speed agitationtype mixer is preferred. More specifically, examples of the high-speedagitation type mixer include a vertical axis rotating type mixer and alateral axis rotating type mixer as mentioned previously, and besides,various apparatuses, such as a high-speed rotation thin-film-typeagitator and a high-speed shear-type agitator. Above all, from theviewpoint of more easily adjusting the desired morphology, a high-speedrotation thin-film-type agitator (also referred to as “thin-filmrotation-type high-speed mixer) is preferred.

Examples of the pulverizer which may be used for the treatment method ofa sulfide solid electrolyte of the present embodiment include apulverizer provided with a rotating body capable of agitating thesulfide solid electrolyte having a volume-based average particlediameter measured by laser diffraction particle size distributionmeasurement of 3 μm or more and a specific surface area measured by theBET method of 20 m²/g or more, namely the precursor for mechanicaltreatment.

In the treatment method of a sulfide solid electrolyte of the presentembodiment, by adjusting a circumferential velocity of the rotating bodyprovided in the pulverizer, the disintegration (atomization) andgranulation (particle growth) of the precursor for mechanical treatmentcan be adjusted, namely the average particle diameter can be decreasedthrough disintegration, or the average particle diameter can beincreased through granulation, and therefore, the morphology of thesulfide solid electrolyte can be readily freely adjusted. Morespecifically, by rotating the rotating body at a low circumferentialvelocity, the disintegration can be achieved, whereas by rotating therotating body at a high circumferential velocity, it becomes possible toachieve the granulation. In this way, only by adjusting thecircumferential velocity of the rotating body, the morphology of thesulfide solid electrolyte can be easily adjusted.

With respect to the circumferential velocity of the rotating body, thelow circumferential velocity or the high circumferential velocity mayvary with, for example, particle diameter, material, and use amount of amedium to be used in the pulverizer, and therefore, it cannot beunequivocally prescribed. For example, in the case of an apparatus notusing a pulverization medium, such as a ball and a bead, as in thehigh-speed rotation thin-film-type agitator, even at a relatively highcircumferential velocity, the disintegration mainly takes place, and thegranulation hardly takes place. On the other hand, in the case of anapparatus using a pulverization medium, such as a ball mill and a beadmill, as mentioned previously, the disintegration can be performed at alow circumferential velocity, and it becomes possible to achieve thegranulation at a high circumferential velocity. In consequence, so longas the predetermined conditions of a pulverization apparatus, thepulverization medium, and so on are identical, the circumferentialvelocity at which the disintegration can be achieved is lower than thecircumferential velocity at which the granulation can be achieved. Inconsequence, for example, under a condition under which the granulationcan be achieved when designating the circumferential velocity of 6 m/sas the boarder, the low circumferential velocity means less than 6 m/s,whereas the high circumferential velocity means 6 m/s or more.

More, specifically, examples of the pulverizer include a medium typepulverizer. The medium type pulverizer is roughly classified into acontainer driving type pulverizer and a medium agitation typepulverizer.

Examples of the container driving type pulverizer include a ball mill orbead mill provided with an agitation tank, a pulverization tank, or acombination thereof. As the ball mill or bead mill, all of varioustypes, such as a rotating type, a rolling type, a vibration type, and aplanetary type, can be adopted.

In addition, examples of the medium agitation type pulverizer includevarious pulverizers, such as an impact type pulverizer, e.g., a cuttermill, a hammer mill, and a pin mill; a tower type pulverizer, e.g., atower mill; an agitation tank type pulverizer, e.g., an attritor, anaquamizer, and a sand grinder; a flow tank type pulverizer, e.g., avisco mill and a pearl mill; a flow tube type pulverizer; an annularpulverizer, e.g., a co-ball-mill; and a continuous dynamic typepulverizer.

In the treatment method of a sulfide solid electrolyte of the presentembodiment, from the viewpoint of more easily adjusting the desiredmorphology, a container driving type pulverizer is preferred, and aboveall, a bead mill and a ball mill are preferred. The container drivingtype pulverizer, such as a bead mill and a ball mill, is provided with,as a rotating body capable of agitating the precursor for mechanicaltreatment, a container for housing the foregoing precursor formechanical treatment, such as an agitation tank and a pulverizationtank. Accordingly, as mentioned previously, the morphology of thesulfide solid electrolyte can be easily adjusted through adjustment ofthe circumferential velocity of the rotating body.

The bead mill or ball mill is also able to adjust the morphology byadjusting the particle diameter, material, and use amount of a bead, aball, or the like to be used, and therefore, it is possible to adjustfiner morphology, and it is also possible to adjust the morphologyunavailable traditionally. For example, as the bead mill, a type that isa centrifugation type and is able to use so-called microbeads of anultrafine particle (about φ0.015 to 1 mm) (for example, Ultra Apex Mill(UAM)).

With respect to the adjustment of the morphology, as the energy to begiven to the precursor for mechanical treatment is made small, namelythe circumferential velocity of the rotating body is decreased, or theparticle diameter of the bead or ball or the like is made small, thereis a tendency that the average particle diameter becomes small(disintegration), and the specific surface area becomes large; whereasas the energy is increased, namely the circumferential velocity of therotating body is increased, or the particle diameter of the bead or ballor the like is made large, there is a tendency that the average particlediameter becomes large (granulation), and the specific surface areabecomes small.

In addition, for example, as the time for mechanical treatment is madelong, the average particle diameter tends to become large (granulation).

The particle diameter of the medium which is used for the bead mill, theball mill, or the like may be appropriately determined taking intoaccount the desired morphology as well as the kind, size, etc. of theapparatus to be used. In general, the particle diameter of the medium ispreferably 0.01 mm or more, more preferably 0.015 mm or more, still morepreferably 0.02 mm or more, and yet still more preferably 0.04 mm ormore, and an upper limit thereof is preferably 3 mm or less, morepreferably 2 mm or less, still more preferably 1 mm or less, and yetstill more preferably 0.8 mm or less.

In addition, examples of a material of the medium include metals, suchas stainless steel, chromium steel, and tungsten carbide; ceramics, suchas zirconia and silicon nitride; and minerals, such as agate.

The treatment time of mechanical treatment may be appropriatelydetermined taking into account the desired morphology as well as thekind, size, etc. of the apparatus to be used. In general, the treatmenttime of mechanical treatment is preferably 5 seconds or more, morepreferably 30 seconds or more, still more preferably 3 minutes or more,and yet still more preferably 15 minutes or more, and an upper limitthereof is preferably 5 hours or less, more preferably 3 hours or less,still more preferably 2 hours or less, and yet still more preferably 1.5hours or less.

The circumferential velocity of the rotating body in the mechanicaltreatment (rotational speed in the apparatus, such a bead mill and aball mill) may be appropriately determined taking into account thedesired morphology as well as the kind, size, etc. of the apparatus tobe used. In general, the circumferential velocity of the rotating bodyis preferably 0.5 m/s or more, more preferably 1 m/s or more, still morepreferably 2 m/s or more, and yet still more preferably 3 m/s or more,and an upper limit thereof is preferably 55 m/s or less, more preferably40 m/s or less, still more preferably 25 m/s or less, and yet still morepreferably 15 m/s or less. In addition, the circumferential velocity maybe even or can be altered on the way.

The mechanical treatment can be performed together with a solvent. Thesolvent can be appropriately selected and used among those exemplifiedabove as the solvent which is used in the Embodiments C and D of theproduction method of a precursor for mechanical treatment. From theviewpoint of obtaining not only the predetermined average particlediameter and specific surface area but also a high ionic conductivitymore stably, as the solvent, an aliphatic hydrocarbon solvent, analicyclic hydrocarbon solvent, an aromatic hydrocarbon solvent, and anether-based solvent are preferred; heptane, cyclohexane, toluene,ethylbenzene, diethyl ether, diisopropyl ether, dibutyl ether,dimethoxyethane, cyclopentylmethyl ether, tert-butylmethyl ether, andanisole are more preferred; heptane, toluene, and ethylbenzene are stillmore preferred; and heptane and toluene are yet still more preferred. Inthe present embodiment, even when a dispersant is not used, theatomization can be readily achieved through disintegration. However,from the viewpoint of more increasing the dispersion and moreefficiently achieving the atomization, a dispersant may be used. Amongthe aforementioned solvents, for example, the ether-based solvent mayfunction as the dispersant.

The use amount of the solvent may be regulated to an amount such thatthe content of the precursor for mechanical treatment relative to thetotal amount of the precursor for mechanical treatment and the solventis preferably 1% by mass or more, more preferably 3% by mass or more,and still more preferably 5% by mass or more, and an upper limit thereofis preferably 30% by mass or less, more preferably 20% by mass or less,and still more preferably 15% by mass or less.

In the case where the precursor for mechanical treatment is an amorphoussolid electrolyte, heat treatment for crystallization becomes necessary.On the other hand, in the case where the precursor for mechanicaltreatment is a crystalline solid electrolyte, heat treatment forcrystallization is basically unnecessary. However, there is a case wherewhile the energy of mechanical treatment is relatively small, a part orthe whole of the crystalline solid electrolyte is vitrified(amorphized). In this case, reheat treatment may be performed. That is,the treatment method of the present embodiment may include heating afterthe mechanical treatment of a precursor for mechanical treatment. Inaddition, in the treatment method of the present embodiment, the heatingmay be performed not only after the mechanical treatment but also beforethe foregoing treatment.

The crystalline solid electrolyte of the present embodiment has amorphology such that different from a primary particle in which a newsurface is exposed through pulverization of a coarse particle,chemically stable primary particles are gathered, and therefore,granulation in the reheat treatment is relatively suppressed. Inconsequence, it is easy to adjust the morphology as compared with aconventional method of atomizing a coarse particle.

In addition, in the treatment method of a sulfide solid electrolyte ofthe present embodiment, it is preferred to obtain the sulfide solidelectrolyte (precursor for mechanical treatment) serving as a rawmaterial for the treatment method, which has a volume-based averageparticle diameter measured by laser diffraction particle sizedistribution measurement of 3 μm or more and a specific surface areameasured by the BET method of 20 m²/g or more through a step includingmixing a raw material inclusion containing a lithium element, a sulfurelement, a phosphorus element, and a halogen element with a complexingagent.

The mixing and the heating in the treatment method of a sulfide solidelectrolyte of the present embodiment are identical with the mixing andthe heating in the production method as mentioned above for theproduction method of a precursor for mechanical treatment. In addition,in the treatment method of a sulfide solid electrolyte of the presentembodiment, the contents other than the mixing and the heating in theproduction method as mentioned above for the production method of aprecursor for mechanical treatment can be appropriately adopted.

In accordance with the treatment of a sulfide solid electrolyte of thepresent embodiment, a sulfide solid electrolyte having the desiredmorphology can be easily produced.

Although the volume-based average particle diameter of the sulfide solidelectrolyte obtained by the treatment method of a sulfide solidelectrolyte of the present embodiment may be adjusted according to thedesire, it is typically 0.05 μm or more, preferably 0.07 μm or more,more preferably 0.1 μm or more, and still more preferably 0.15 μm ormore, and an upper limit thereof is typically 50 μm or less, preferably30 μm or less, more preferably 20 μm or less, still more preferably 15μm or less, and yet still more preferably 10 μm or less.

In addition, although the specific surface area of the foregoing sulfidesolid electrolyte may also be adjusted according to the desire, it istypically 0.1 m²/g or more, preferably 0.3 m²/g or more, more preferably0.5 m²/g or less, and still more preferably 1 m²/g or more, and an upperlimit thereof is typically 70 m²/g or less, preferably 50 m²/g or less,more preferably 45 m²/g or less, and still more preferably 40 m²/g orless.

(Application of Sulfide Solid Electrolyte)

The sulfide solid electrolyte obtained by the treatment method of asulfide solid electrolyte of the present embodiment has the desiredmorphology according to an application and can be used for the sameapplication as the application described above in the section of“Application of Sulfide Solid Electrolyte” (which may also be called anapplication of precursor for mechanical treatment). That is, the sulfidesolid electrolyte obtained by the treatment method of a sulfide solidelectrolyte of the present embodiment can be used for a positiveelectrode layer, a negative electrode layer, and an electrolyte layer inan all-solid-state lithium battery.

EXAMPLES

Next, the present invention is described specifically with reference toExamples, but it should be construed that the present invention is by nomeans restricted by these Examples.

Production Example 1

In a one-liter impeller-provided reaction tank, 15.3 g of lithiumsulfide and 24.7 g of diphosphorus pentasulfide were added in a nitrogenatmosphere. After actuating the impeller, 400 mL of tetrahydrofuranwhich had been previously cooled to −20° C. was introduced into thecontainer. After naturally raising the temperature to room temperature(23° C.), agitation was continued for 72 hours, the obtained reactionliquid slurry was charged in a glass filter (pore size: 40 to 100 μm) toobtain a solid component, and then, the solid component was dried at 90°C., thereby obtaining 38 g of Li₃PS₄ (purity: 90% by mass) as a whitepowder. The obtained powder was subjected to powder X-ray diffractometry(XRD) with an X-ray diffraction (XRD) apparatus (SmartLab apparatus,manufactured Rigaku Corporation). As a result, the foregoing powderexpressed a hallow pattern and confirmed to be amorphous Li₃PS₄.

Example 1

Into a stirring bar-containing Schlenk flask (capacity: 100 mL), 1.70 gof the white powder (Li₃PS₄: 1.53 g) obtained in Production Example 1,0.19 g of lithium bromide, and 0.28 g of lithium iodide were introducedin a nitrogen atmosphere. After rotating the stirring bar, 20 mL oftetramethylethylenediamine (TMEDA) as a complexing agent was added,agitation was continued for 12 hours, and the obtained electrolyteprecursor inclusion was dried in vacuo (at room temperature: 23° C.) toobtain an electrolyte precursor as a powder. Subsequently, the powder ofthe electrolyte precursor was heated at 120° C. in vacuo for 2 hours,thereby obtaining an amorphous solid electrolyte. Furthermore, theamorphous solid electrolyte was heated at 140° C. in vacuo for 2 hours,thereby obtaining a crystalline solid electrolyte (the heatingtemperature for obtaining a crystalline solid electrolyte (140° C. inthis Example) will be sometimes referred to as “crystallizationtemperature”).

A part of each of the obtained powder of the electrolyte precursor andcrystalline solid electrolyte was dissolved in methanol, the obtainedmethanol solution was subjected to gas chromatographic analysis tomeasure the content of tetramethylethylenediamine. The content of thecomplexing agent in the electrolyte precursor was 55.0% by mass, and thecontent of the complexing agent in the crystalline solid electrolyte was1.2% by mass.

The obtained electrolyte precursor, amorphous solid electrolyte, andcrystalline solid electrolyte were subjected to powder X-raydiffractometry (XRD) with an X-ray diffraction (XRD) apparatus (SmartLabapparatus, manufactured Rigaku Corporation), and X-ray diffractionspectra are shown in FIG. 3. In addition, the obtained amorphous solidelectrolyte was subjected to composition analysis through ICP analysis(inductively coupled plasma atomic emission spectrophotometry). As aresult of the composition analysis, the contents of Li, P, S, Br, and Iwere found to be 10.1% by mass, 13.2% by mass, 55.2% by mass, 8.4% bymass, and 13.1% by mass, respectively.

In the X-ray diffraction spectrum of the electrolyte precursor, peaksdifferent from the peaks derived from the used raw materials wereobserved, and an X-ray diffraction pattern different from those of theamorphous solid electrolyte and the crystalline solid electrolyte wasshown. In addition, the raw materials used in this Example 1 (amorphousLi₃PS₄, lithium bromide, and lithium iodide) and the raw materials usedin other Examples (lithium sulfide, diphosphorus pentasulfide, andcrystalline Li₃PS₄) were also subjected to powder X-ray diffractometry(XRD), and X-ray diffraction spectra are shown in FIG. 4. The X-raydiffraction spectrum of the electrolyte precursor showed an X-raydiffraction pattern different from the X-ray diffraction spectra of theraw materials.

In the X-ray diffraction spectrum of the amorphous solid electrolyte,any peak other than the peaks derived from the raw materials wasconfirmed to be absent. In addition, in the X-ray diffraction spectrumof the crystalline solid electrolyte, crystallization peaks weredetected at 2θ=20.2° and 23.6°, and the crystalline solid electrolytehad a thio-LISICON Region II-type crystal structure. An ionicconductivity of the crystalline solid electrolyte was measured and foundto be 2.90×10⁻³ (S/cm), and the crystalline solid electrolyte wasconfirmed to have a high ionic conductivity. A half width Δ2θ of amaximum peak (2θ=20.2°) including the background at 2θ=10 to 40° was0.25.

In this Example, the measurement of the ionic conductivity was performedin the following manner.

From the obtained crystalline solid electrolyte, a circular pellethaving a diameter of 10 mm (cross-sectional area S: 0.785 cm²) and aheight (L) of 0.1 to 0.3 cm was molded to prepare a sample. From the topand the bottom of the sample, electrode terminals were taken, and theion conductivity was measured according to an alternate currentimpedance method (frequency range: 5 MHz to 0.5 Hz, amplitude: 10 mV) togive a Cole-Cole plot. In the vicinity of the right end of the arcobserved in the high-frequency side region, a real number part Z′ (Ω) atthe point at which —Z″ (Ω) is the smallest was referred to as a bulkresistance R (Ω) of the electrolyte, and according to the followingequation, the ion conductivity o (S/cm) was calculated.

R=ρ(L/S)

o=1/ρ

The obtained crystalline solid electrolyte had a volume-based averageparticle diameter of 10.5 μm and a specific surface area of 25 m²/g.

The average diameter was measured with a laser diffraction/scatteringparticle diameter distribution measuring device (“Partica LA-950 (modelnumber), manufactured by HORIBA, Ltd.). In addition, the specificsurface area was a value measured by the BET dynamic method (three-pointmethod) using a nitrogen gas as an adsorbate in conformity with JISR1626:1996.

Example 2

Into a one-liter impeller-provided reaction tank, 42.6 g of the whitepowder (Li₃PS₄. 38.3 g) obtained in Production Example 1, 4.6 g oflithium bromide, and 7.1 g of lithium iodide were introduced in anitrogen atmosphere. After rotating the impeller, 473 mL of dibutylether as a solvent and 111 mL of N,N,N′,N′-tetramethylethylenediamine(TMEDA) as a complexing agent were charged, and agitation was continuedfor 24 hours. Subsequently, 433 mL of dibutyl ether was added, and then,pulverization treatment was performed using a circulation-operable beadmill (“STAR MILL LMZ015 (a trade name)”, manufactured by AshizawaFinetech Ltd.) for 3 hours under a predetermined condition (beadmaterial: zirconia, bead diameter: 0.5 mmφ, use amount of bead: 456 g,pump flow rate: 650 mL/min, circumferential velocity: 8 m/s, mill jackettemperature: 20° C.). The obtained slurry was dried in vacuo (roomtemperature: 23° C.) to obtain an electrolyte precursor as a powder.Subsequently, the powder of the electrolyte precursor was heated at 120°C. in vacuo for 2 hour, thereby obtaining a white powder of an amorphoussolid electrolyte. The average particle diameter (D₅₀) and the specificsurface area of the obtained amorphous solid electrolyte are shown inTable 1.

Example 3

The white powder obtained in Example 2 was further heated in vacuo at160° C. for 2 hours, to obtain a white powder of a crystalline solidelectrolyte. The average particle diameter (D₅₀), the specific surfacearea, and the ionic conductivity of the obtained crystalline solidelectrolyte are shown in Table 1.

Example 4

Into a one-liter impeller-provided reaction tank, 14.7 g of lithiumsulfide, 23.6 g of diphosphorus pentasulfide, 4.6 g of lithium bromide,and 7.1 g of lithium iodide were introduced in a nitrogen atmosphere.After rotating the impeller, 467 mL of cyclohexane as a solvent and 111mL of N,N,N′,N′-tetramethylethylenediamine (TMEDA) as a complexing agentwere charged, and agitation was continued for 72 hours. Subsequently,428 mL of cyclohexane was added, and then, pulverization treatment wasperformed using a circulation-operable bead mill (“STAR MILL LMZ015 (atrade name)”, manufactured by Ashizawa Finetech Ltd.) for 3 hours undera predetermined condition (bead material: zirconia, bead diameter: 0.5mmφ, use amount of bead: 456 g, pump flow rate: 650 mL/min,circumferential velocity: 8 m/s, mill jacket temperature: 20° C.). Theobtained slurry was dried in vacuo (room temperature: 23° C.) to obtainan electrolyte precursor as a powder. Subsequently, the powder of theelectrolyte precursor was heated at 120° C. in vacuo for 2 hour, therebyobtaining a white powder of an amorphous solid electrolyte. The averageparticle diameter (D₅₀) and the specific surface area of the obtainedamorphous solid electrolyte are shown in Table 1.

Example 5

The white powder obtained in Example 4 was further heated in vacuo at160° C. for 2 hours, to obtain a white powder of a crystalline solidelectrolyte. The obtained crystalline sulfide solid electrolyte wasphotographed with a scanning electron microscope (SEM). The photographedimage is shown in FIG. 7. The average particle diameter (D₅₀), thespecific surface area, and the ionic conductivity of the obtainedcrystalline solid electrolyte are shown in Table 1.

Example 6

In a treatment container of a thin-film rotation-type high-speed mixer(“FILMIX FM-56 (a trade name), manufactured by PRIMIX Corporation), 8.0g of the white powder obtained in Example 5 and 72 g of toluene werecharged in a nitrogen atmosphere, and then, dispersion treatment wasperformed at a circumferential velocity of 50 m/s for 1 minute. Theobtained slurry was dried in vacuo (room temperature: 23° C.) to obtaina white powder of a crystalline solid electrolyte. The obtainedcrystalline sulfide solid electrolyte was photographed with a scanningelectron microscope (SEM). The photographed image is shown in FIG. 8.The average particle diameter (D₅₀), the specific surface area, and theionic conductivity of the obtained crystalline solid electrolyte areshown in Table 1.

Example 7

In a 0.5-liter impeller-provided reaction tank, 30.0 g of the whitepowder obtained in Example 5 and 470 g of heptane were charged in anitrogen atmosphere. After rotating the impeller, pulverizationtreatment was performed using a circulation-operable bead mill (“STARMILL LMZ015 (a trade name)”, manufactured by Ashizawa Finetech Ltd.) for1 hour under a predetermined condition (bead material: zirconia, beaddiameter: 0.5 mmφ, use amount of bead: 456 g, pump flow rate: 650mL/min, circumferential velocity: 8 m/s, mill jacket temperature: 20°C.). The obtained slurry was dried in vacuo (room temperature: 23° C.)to obtain a white powder of an amorphous solid electrolyte. The obtainedamorphous sulfide solid electrolyte was photographed with a scanningelectron microscope (SEM). The photographed image is shown in FIG. 9.The average particle diameter (D₅₀) and the specific surface area areshown in Table 1.

Example 8

After performing the pulverization treatment in the same manner as inExample 7, the slurry was charged in a one-liter impeller-providedpressure-resistant jacketed reaction tank. The container washermetically sealed, and the impeller was rotated. Then, a heatingmedium was passed through the jacket, an internal temperature of theslurry was kept at 140° C., and agitation was continued for 1 hour. Theobtained slurry was dried in vacuo (room temperature: 23° C.) to obtaina white powder of a crystalline solid electrolyte. The average particlediameter (D₅₀), the specific surface area, and the ionic conductivity ofthe obtained crystalline solid electrolyte are shown in Table 1.

Example 9

The white powder obtained in Example 7 was heated in vacuo at 160° C.for 1 hour, to obtain a white powder of a crystalline solid electrolyte.The average particle diameter (D₅₀), the specific surface area, and theionic conductivity of the obtained crystalline solid electrolyte areshown in Table 1.

Example 10

In a 0.5-liter impeller-provided reaction tank, 30.0 g of the whitepowder obtained in Example 5 and 470 g of toluene were charged in anitrogen atmosphere. After rotating the impeller, pulverizationtreatment was performed using a circulation-operable bead mill (“STARMILL LMZ015 (a trade name)”, manufactured by Ashizawa Finetech Ltd.) for30 minutes under a predetermined condition (bead material: zirconia,bead diameter: 0.5 mmφ, use amount of bead: 456 g, pump flow rate: 650mL/min, circumferential velocity: 4 m/s, mill jacket temperature: 20°C.). The obtained slurry was dried in vacuo (room temperature: 23° C.)to obtain a white powder of an amorphous solid electrolyte. In addition,the average particle diameter (D₅₀) and the specific surface area of theobtained amorphous solid electrolyte are shown in Table 1.

Example 11

In a 0.5-liter impeller-provided reaction tank, 30.0 g of the whitepowder obtained in Example 5 and 470 g of toluene were charged in anitrogen atmosphere. After rotating the impeller, pulverizationtreatment was performed using a circulation-operable bead mill (“STARMILL LMZ015 (a trade name)”, manufactured by Ashizawa Finetech Ltd.) for1 hour under a predetermined condition (bead material: zirconia, beaddiameter: 0.5 mmφ, use amount of bead: 456 g, pump flow rate: 650mL/min, circumferential velocity: 4 m/s, mill jacket temperature: 20°C.). The obtained slurry was dried in vacuo (room temperature: 23° C.)to obtain a white powder of an amorphous solid electrolyte. The averageparticle diameter (D₅₀) and the specific surface area of the obtainedamorphous solid electrolyte are shown in Table 1.

Example 12

In a 0.5-liter impeller-provided reaction tank, 30.0 g of the whitepowder obtained in Example 5 and 470 g of toluene were charged in anitrogen atmosphere. After rotating the impeller, pulverizationtreatment was performed using a circulation-operable bead mill (“STARMILL LMZ015 (a trade name)”, manufactured by Ashizawa Finetech Ltd.) for2.5 hours under a predetermined condition (bead material: zirconia, beaddiameter: 0.3 mmφ, use amount of bead: 456 g, pump flow rate: 650mL/min, circumferential velocity: 8 m/s, mill jacket temperature: 20°C.). The obtained slurry was dried in vacuo (room temperature: 23° C.)to obtain a white powder of an amorphous solid electrolyte. The averageparticle diameter (D₅₀) and the specific surface area of the obtainedamorphous solid electrolyte are shown in Table 1.

Example 13

In a 0.5-liter impeller-provided reaction tank, 30.0 g of the whitepowder obtained in Example 5 and 470 g of toluene were charged in anitrogen atmosphere. After rotating the impeller, pulverizationtreatment was performed using a circulation-operable bead mill (“STARMILL LMZ015 (a trade name)”, manufactured by Ashizawa Finetech Ltd.) for2.5 hours under a predetermined condition (bead material: zirconia, beaddiameter: 0.3 mmφ, use amount of bead: 456 g, pump flow rate: 650mL/min, circumferential velocity: 12 m/s, mill jacket temperature: 20°C.). The obtained slurry was dried in vacuo (room temperature: 23° C.)to obtain a white powder of an amorphous solid electrolyte. The averageparticle diameter (D₅₀) and the specific surface area of the obtainedamorphous solid electrolyte are shown in Table 1.

Example 14

In a 0.5-liter impeller-provided reaction tank, 30.0 g of the whitepowder obtained in Example 5 and 470 g of toluene were charged in anitrogen atmosphere. After rotating the impeller, pulverizationtreatment was performed using a circulation-operablemicrobeads-compatible bead mill (“UAM-015 (model number)”, manufacturedby Hiroshima Metal & Machinery Co., Ltd.) for 30 minutes under apredetermined condition (bead material: zirconia, bead diameter: 0.1mmφ, use amount of bead: 391 g, pump flow rate: 150 mL/min,circumferential velocity: 8 m/s, mill jacket temperature: 20° C.). Theobtained slurry was dried in vacuo (room temperature: 23° C.) to obtaina white powder of an amorphous solid electrolyte. The average particlediameter (D₅₀) and the specific surface area of the obtained amorphoussolid electrolyte are shown in Table 1.

Example 15

In a 0.5-liter impeller-provided reaction tank, 30.0 g of the whitepowder obtained in Example 5 and 470 g of toluene were charged in anitrogen atmosphere. After rotating the impeller, first pulverizationtreatment was performed using a circulation-operablemicrobeads-compatible bead mill (“UAM-015 (model number)”, manufacturedby Hiroshima Metal & Machinery Co., Ltd.) for 30 minutes under apredetermined condition (bead material: zirconia, bead diameter: 0.05mmφ, use amount of bead: 391 g, pump flow rate: 150 mL/min,circumferential velocity: 8 m/s, mill jacket temperature: 20° C.).Subsequently, the circumferential velocity was changed to 12.5 m/s, andsecond pulverization treatment was performed for 10 minutes. Theobtained slurry was dried in vacuo (room temperature: 23° C.) to obtaina white powder of an amorphous solid electrolyte. The average particlediameter (D₅₀) and the specific surface area of the obtained amorphoussolid electrolyte are shown in Table 1.

Example 16

In a 0.5-liter impeller-provided reaction tank, 30.0 g of the whitepowder obtained in Example 5 and 470 g of toluene were charged in anitrogen atmosphere. After rotating the impeller, first pulverizationtreatment was performed using a circulation-operablemicrobeads-compatible bead mill (“UAM-015 (model number)”, manufacturedby Hiroshima Metal & Machinery Co., Ltd.) for 80 minutes under apredetermined condition (bead material: zirconia, bead diameter: 0.05mmφ, use amount of bead: 391 g, pump flow rate: 150 mL/min,circumferential velocity: 12 m/s, mill jacket temperature: 20° C.).Subsequently, the circumferential velocity was changed to 10 m/s, andsecond pulverization treatment was performed for 10 minutes. Theobtained slurry was dried in vacuo (room temperature: 23° C.) to obtaina white powder of an amorphous solid electrolyte. The average particlediameter (D₅₀) and the specific surface area of the obtained amorphoussolid electrolyte are shown in Table 1.

Example 17

In a 0.5-liter impeller-provided reaction tank, 30.0 g of the whitepowder obtained in Example 5, 313 g of heptane, and 157 g of dibutylether were charged in a nitrogen atmosphere. After rotating theimpeller, first pulverization treatment was performed using acirculation-operable microbeads-compatible bead mill (“UAM-015 (modelnumber)”, manufactured by Hiroshima Metal & Machinery Co., Ltd.) for 25minutes under a predetermined condition (bead material: zirconia, beaddiameter: 0.05 mmφ, use amount of bead: 391 g, pump flow rate: 150mL/min, circumferential velocity: 8 m/s, mill jacket temperature: 20°C.). Subsequently, the circumferential velocity was changed to 12 m/s,and second pulverization treatment was performed for 25 minutes. Theobtained slurry was dried in vacuo (room temperature: 23° C.) to obtaina white powder of an amorphous solid electrolyte. The average particlediameter (D₅₀) and the specific surface area of the obtained amorphoussolid electrolyte are shown in Table 1.

Example 18

In a 0.5-liter impeller-provided reaction tank, 30.0 g of the whitepowder obtained in Example 5, 447 g of heptane, and 24 g of dibutylether were charged in a nitrogen atmosphere. After rotating theimpeller, pulverization treatment was performed using acirculation-operable microbeads-compatible bead mill (“UAM-015 (modelnumber)”, manufactured by Hiroshima Metal & Machinery Co., Ltd.) for 25minutes under a predetermined condition (bead material: zirconia, beaddiameter: 0.05 mm, use amount of bead: 391 g, pump flow rate: 150mL/min, circumferential velocity: 8 m/s, mill jacket temperature: 20°C.). The obtained slurry was dried in vacuo (room temperature: 23° C.)to obtain a white powder of an amorphous solid electrolyte. The averageparticle diameter (D₅₀) and the specific surface area of the obtainedamorphous solid electrolyte are shown in Table 1.

Example 19

In a 0.5-liter impeller-provided reaction tank, 30.0 g of the whitepowder obtained in Example 5, 461 g of heptane, and 9 g of dibutyl etherwere charged in a nitrogen atmosphere. After rotating the impeller,pulverization treatment was performed using a circulation-operablemicrobeads-compatible bead mill (“UAM-015 (model number)”, manufacturedby Hiroshima Metal & Machinery Co., Ltd.) for 25 minutes under apredetermined condition (bead material: zirconia, bead diameter: 0.05mmφ, use amount of bead: 391 g, pump flow rate: 150 mL/min,circumferential velocity: 8 m/s, mill jacket temperature: 20° C.). Theobtained slurry was dried in vacuo (room temperature: 23° C.) to obtaina white powder of an amorphous solid electrolyte. The average particlediameter (D₅₀) and the specific surface area of the obtained amorphoussolid electrolyte are shown in Table 1.

Example 20

In a 0.5-liter impeller-provided reaction tank, 30.0 g of the whitepowder obtained in Example 4 and 470 g of heptane were charged in anitrogen atmosphere. After rotating the impeller, first pulverizationtreatment was performed using a circulation-operablemicrobeads-compatible bead mill (“UAM-015 (model number)”, manufacturedby Hiroshima Metal & Machinery Co., Ltd.) for 35 minutes under apredetermined condition (bead material: zirconia, bead diameter: 0.05mmi, use amount of bead: 391 g, pump flow rate: 150 mL/min,circumferential velocity: 8 m/s, mill jacket temperature: 20° C.).Subsequently, the circumferential velocity was changed to 10 m/s, andsecond pulverization treatment was performed for 10 minutes. Theobtained slurry was dried in vacuo (room temperature: 23° C.) to obtaina white powder of an amorphous solid electrolyte. The average particlediameter (D₅₀) and the specific surface area of the obtained amorphoussolid electrolyte are shown in Table 1.

Comparative Example 1

Into a one-liter impeller-provided reaction tank, 20.5 g of lithiumsulfide, 33.1 g of diphosphorus pentasulfide, 6.5 g of lithium bromide,and 10.0 g of lithium iodide were added in a nitrogen atmosphere. Afterrotating the impeller, 630 g of toluene was introduced, and this slurrywas agitated for 10 minutes. Pulverization treatment was performed usinga circulation-operable bead mill (“STAR MILL LMZ015 (a trade name)”,manufactured by Ashizawa Finetech Ltd.) for 45 hours under apredetermined condition (bead material: zirconia, bead diameter: 0.5mmφ, use amount of bead: 456 g, pump flow rate: 650 mL/min,circumferential velocity: 12 m/s, mill jacket temperature: 45° C.). Theobtained slurry was dried in vacuo (room temperature: 23° C.) to obtaina white powder of an amorphous solid electrolyte. The average particlediameter (D₅₀) and the specific surface area of the obtained amorphoussolid electrolyte are shown in Table 1.

Comparative Example 2

The white powder obtained in Comparative Example 1 was further heated invacuo at 210° C. for 2 hours, to obtain a white powder of a crystallinesolid electrolyte. In the X-ray diffraction spectrum of the crystallinesolid electrolyte, crystallization peaks were detected at 2θ=20.2° and23.6°, and the crystalline solid electrolyte was confirmed to have athio-LISICON Region II-type crystal structure. A half width Δ2θ of amaximum peak (2θ=20.2°) including the background at 2θ=10 to 40 was0.34. The average particle diameter (D₅₀), the specific surface area,and the ionic conductivity of the obtained crystalline solid electrolyteare shown in Table 1.

Comparative Example 3

In a 0.5-liter impeller-provided reaction tank, 30.0 g of the whitepowder obtained in Comparative Example 1 and 470 g of toluene werecharged in a nitrogen atmosphere. After rotating the impeller, firstpulverization treatment was performed using a circulation-operablemicrobeads-compatible bead mill (“UAM-015 (model number)”, manufacturedby Hiroshima Metal & Machinery Co., Ltd.) for 20 minutes under apredetermined condition (bead material: zirconia, bead diameter: 0.05mmφ, use amount of bead: 391 g, pump flow rate: 150 mL/min,circumferential velocity: 8 m/s, mill jacket temperature: 20° C.).Subsequently, the circumferential velocity was changed to 12 m/s, andsecond pulverization treatment was performed for 25 minutes. Theobtained slurry was dried in vacuo (room temperature: 23° C.) to obtaina white powder of an amorphous solid electrolyte. The average particlediameter (D₅₀) and the specific surface area of the obtained amorphoussolid electrolyte are shown in Table 1.

Comparative Example 4

In a 0.5-liter impeller-provided reaction tank, 30.0 g of the whitepowder obtained in Comparative Example 1 and 470 g of toluene werecharged in a nitrogen atmosphere. After rotating the impeller, firstpulverization treatment was performed using a circulation-operablemicrobeads-compatible bead mill (“UAM-015 (model number)”, manufacturedby Hiroshima Metal & Machinery Co., Ltd.) for 20 minutes under apredetermined condition (bead material: zirconia, bead diameter: 0.05mmi, use amount of bead: 391 g, pump flow rate: 150 mL/min,circumferential velocity: 8 m/s, mill jacket temperature: 20° C.).Subsequently, the circumferential velocity was changed to 12 m/s, andsecond pulverization treatment was performed for 15 minutes. Theobtained slurry was dried in vacuo (room temperature: 23° C.) to obtaina white powder of an amorphous solid electrolyte. The average particlediameter (D₅₀) and the specific surface area of the obtained amorphoussolid electrolyte are shown in Table 1.

TABLE 1 Average particle Specific Ionic diameter surface areaconductivity μm m²/g mS/cm Example 1 10.5 25 2.9 2 6.4 34 — 3 8.2 36 4.14 5.4 32 — 5 8.6 39 4.1 6 0.3 36 3.3 7 5.6 6 — 8 5.9 6 3.4 9 6.2 5 3.810 1.8 31 — 11 2.4 19 — 12 2.0 17 — 13 2.2 15 — 14 1.9 9 — 15 3.0 7 — 161.5 15 — 17 1.0 41 — 18 0.6 24 — 19 0.8 12 — 20 1.1 12 — Comparative 14.5 3 — Example 2 6.6 2 4.5 3 4.7 3 4 5.9 3 —

Even in the case of an extremely small fine particle as 0.3 μm as inExample 6 in which the precursor for mechanical treatment of Example 5(average particle diameter: 8.6 μm) was subjected to disintegrationthrough mechanical treatment, the reduction of the ionic conductivitywas suppressed, and a high ionic conductivity was revealed. Furthermore,as noted from Examples 7 to 9, even in the case where the solidelectrolyte resulting from vitrification of apart or the whole of theprecursor for mechanical treatment through mechanical treatment isrecrystallized, the change in morphology is small. In consequence, it ispossible to easily control the morphology through adjustment bymechanical treatment. On the other hand, in the Comparative Examples notusing the precursor for mechanical treatment of the present embodiment,even when performing the same mechanical treatment as in the presentExamples, the morphology could not be adjusted. From the foregoingresults, it has been confirmed that in view of the fact that the sulfidesolid electrolyte of the present embodiment has such properties that theaverage particle diameter is 3 μm or more, and the specific surface areais 20 m²/g, the sulfide solid electrolyte of the present embodiment isone which is able to adjust the morphology unavailable traditionally, oris readily adjusted to have the desired morphology through mechanicaltreatment.

INDUSTRIAL APPLICABILITY

The sulfide solid electrolyte of the present embodiment is one which isable to adjust the morphology unavailable traditionally, or is readilyadjusted to have the desired morphology, and has a high ionicconductivity and an excellent battery performance. The treatment methodof a solid electrolyte of the present embodiment is able to provide asolid electrolyte which is adjusted to have the desired morphology.Accordingly, the solid electrolyte according to the present embodimentis suitably used for batteries, especially batteries forinformation-related instruments, communication instruments, and so on,such as personal computers, video cameras and mobile phones.

1. A sulfide solid electrolyte having a volume-based average particlediameter measured by laser diffraction particle size distributionmeasurement of 3 μm or more and a specific surface area measured by aBET method of 20 m²/g or more.
 2. The sulfide solid electrolyte of claim1, which is a precursor suitable for at least one mechanical treatmentselected from the group consisting of disintegration and granulation. 3.The sulfide solid electrolyte of claim 1, comprising a lithium element,a sulfur element, a phosphorus element, and a halogen element.
 4. Thesulfide solid electrolyte of claim 1, which is amorphous or crystalline.5. The sulfide solid electrolyte of claim 1, which is crystalline. 6.The sulfide solid electrolyte of claim 4, wherein a half width of amaximum peak including a background at 2θ=10 to 40° in X-raydiffractometry using a CuKα ray is Δ2θ=0.32 or less.
 7. The sulfidesolid electrolyte of claim 1, having a thio-LISICON Region II-typecrystal structure.
 8. A method of treating a sulfide solid electrolyte,the method comprising subjecting a sulfide solid electrolyte having avolume-based average particle diameter measured by laser diffractionparticle size distribution measurement of 3 μm or more and a specificsurface area measured by a BET method of 20 m2/g or more to at least onemechanical treatment selected from the group consisting ofdisintegration and granulation.
 9. The method of claim 8, wherein the atleast one mechanical treatment is performed with a pulverizer or anagitator.
 10. The method of claim 8, wherein the at least one mechanicaltreatment is performed using a solvent.
 11. The method of claim 8,wherein the at least one mechanical treatment is performed with a ballmill, a bead mill, or a high-speed rotation thin-film-type agitator. 12.The method of claim 8, wherein the at least one mechanical treatment isperformed with a pulverizer provided with a rotating body capable ofagitating the sulfide solid electrolyte, and a circumferential velocityof the rotating body is adjusted, thereby adjusting the disintegrationor granulation of the sulfide solid electrolyte in the at least onemechanical treatment.
 13. The method of claim 12, wherein the rotatingbody is rotated at a low circumferential velocity, to achieve thedisintegration, or the rotating body is rotated at a highcircumferential velocity, to achieve the granulation.
 14. The method ofclaim 8, wherein the at least one mechanical treatment is performed witha high-speed rotation thin-film-type agitator.
 15. The method of claim8, further comprising heating after the at least one mechanicaltreatment.
 16. The method of claim 8, wherein the sulfide solidelectrolyte is obtained through a process comprising mixing a rawmaterial inclusion comprising a lithium element, a sulfur element, aphosphorus element, and a halogen element with a complexing agent. 17.The method of claim 16, wherein the process comprises pulverizing anelectrolyte precursor obtained through the mixing.
 18. The method ofclaim 16, wherein the process comprises heating an electrolyte precursorobtained through the mixing, or an electrolyte precursor pulverizedproduct obtained through pulverizing the electrolyte precursor.
 19. Thesulfide solid electrolyte of claim 1, having a volume-based averageparticle diameter measured by laser diffraction particle sizedistribution measurement of 150 μm or less.